全文获取类型
收费全文 | 13368篇 |
免费 | 208篇 |
国内免费 | 11篇 |
专业分类
教育 | 9217篇 |
科学研究 | 1676篇 |
各国文化 | 116篇 |
体育 | 994篇 |
综合类 | 28篇 |
文化理论 | 160篇 |
信息传播 | 1396篇 |
出版年
2022年 | 93篇 |
2021年 | 135篇 |
2020年 | 203篇 |
2019年 | 271篇 |
2018年 | 393篇 |
2017年 | 417篇 |
2016年 | 378篇 |
2015年 | 251篇 |
2014年 | 366篇 |
2013年 | 2170篇 |
2012年 | 323篇 |
2011年 | 304篇 |
2010年 | 296篇 |
2009年 | 259篇 |
2008年 | 278篇 |
2007年 | 285篇 |
2006年 | 269篇 |
2005年 | 230篇 |
2004年 | 261篇 |
2003年 | 228篇 |
2002年 | 239篇 |
2001年 | 314篇 |
2000年 | 333篇 |
1999年 | 253篇 |
1998年 | 139篇 |
1997年 | 181篇 |
1996年 | 175篇 |
1995年 | 119篇 |
1994年 | 130篇 |
1993年 | 118篇 |
1992年 | 202篇 |
1991年 | 187篇 |
1990年 | 213篇 |
1989年 | 211篇 |
1988年 | 180篇 |
1987年 | 192篇 |
1986年 | 175篇 |
1985年 | 211篇 |
1984年 | 150篇 |
1983年 | 131篇 |
1982年 | 124篇 |
1981年 | 109篇 |
1980年 | 112篇 |
1979年 | 178篇 |
1978年 | 131篇 |
1977年 | 113篇 |
1975年 | 92篇 |
1974年 | 94篇 |
1973年 | 91篇 |
1971年 | 89篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
911.
912.
913.
Michael J. Kurtz Guenther Eichhorn Alberto Accomazzi Carolyn Grant Markus Demleitner Edwin Henneken Stephen S. Murray 《Information processing & management》2005,41(6):1395-1402
It has been shown (Lawrence, S. (2001). Online or invisible? Nature, 411, 521) that journal articles which have been posted without charge on the internet are more heavily cited than those which have not been. Using data from the NASA Astrophysics Data System (ads.harvard.edu) and from the ArXiv e-print archive at Cornell University (arXiv.org) we examine the causes of this effect. 相似文献
914.
915.
Herman S D'Souza Geraldine Menezes T Venkatesh 《Indian journal of clinical biochemistry : IJCB》2002,17(1):1-4
Our study aimed at comparing lead and zinc protoporphyrin (ZPP) levels in capillary and venous blood samples in a small population
and to employ an easier method of sample collection for a major screening program in school children in major Indian cities.
An awareness program on lead and its effects was conducted in two different schools. A total of thirty urban school children
from South India, with an age group between 4–12 years consented for dual blood sampling and reported for the study. Venous
and capillary blood samples were obtained simultaneously. Blood lead and zinc protoporphyrin (ZPP) levels were estimated using
ESA Lead Analyzer and Haematofluorometer respectively. A significant correlation between capillary and venous ZPP (r=0.98)
and lead (r=0.99) was observed. Rank sum test showed that there is no statistically significant difference between capillary
and venous ZPP (P=0.891) and lead (P=0.672) values. This pilot study recommends that screening for lead may be done using
capillary blood samples since significant correlation is observed between capillary and venous blood measurements. Obtaining
samples using this mode is a non-invasive, less expensive, quick and easy method in children. Appropriately performed capillary
sampling may be considered as an acceptable alternative to venipuncture for screening of blood for lead poisoning both in
children and adults. 相似文献
916.
Ishrat Kareem S. A. Jaweed J. S. Bardapurkar V. P. Patil 《Indian journal of clinical biochemistry : IJCB》2004,19(2):124-127
The present study was undertaken in 100 subjects, 30 diabetics without complication (group I), 40 diabetics with retinopathy
(group II) and 30 non diabetic as normal control group (group III). Blood sugar levels, magnesium, cholesterol and triglyceride
were analyzed from plasma and serum. The results were correlated with degree of diabetic control from the levels of glycosylated
hemoglobin. Serum magnesium levels in group II were found to be significantly lowered than in group I. There was also significant
difference in magnesium levels of group I and group III. We found a significant correlation between the glycosylated hemoglobin
and magnesium levels in our study.
The results also indicate that the patients with diabetic retinopathy showed significant rise in serum cholesterol and triglyceride.
Probably hypomagnesemia and increased serum cholesterol and triglyceride levels are responsible for microvascular changes
in diabetes leading to retinopathy. The purpose of this study was thus to gather information about the degree of control of
diabetes and magnesium status. 相似文献
917.
The problem factorizing (separating) the transfer function of a given SISO 3-D discrete system, ie of a system depending on three independent variables, is considered. The 3-D system is assumed to be available in its transfer function representation, which is converted to a canonical state-space model by a simple inspection procedure. Then applying state-feedback to this canonical model we choose the feedback matrix gain (under certain conditions) such that the transfer function of the closed-loop system has the desireed factorized form, ie a product of three 1-D transfer functions each one being dependent on a single variable. The method is illustrated by a nontrivial numerical example. 相似文献
918.
Until comparatively recently the purification of sea or brackish water depended largely on some form of distillation. In recent years, however, a number of industrial concerns have directed increasing attention to processes depending on reverse osmosis. A number of large plants have been installed and this article reviews the present state of reverse osmosis technology and the factors determining its efficiency. Its advantages include its relatively low fuel consumption, and in this respect further substantial savings are in prospect. 相似文献
919.
Serum free fatty acids (FFA) in 100 parturient (50 primiparous and 50 multiparous volunteers) and 50 female patient (30 patients 20–30 years age group and 20 patients 31–50 yrs age group) volunteers undergoing elective major abdominal surgery were monitored during different stages of delivery and surgery respectively. FFA increased in both primiparous and multiparous from full term (46 mg%) to second stage of labour (60 mg%) and gradually decreased to 38 mg% on the third day postpartum. The intergroup comparison between primiparous and multiparous was significant. Surgical stress also increased FFA from the day of admission (21 mg%) to the preoperative stage (35 mg%). The intergroup comparison between 20–30 yrs age group and 31–50 yrs age group did not show any significant change. 相似文献
920.
G. Kusumanjali Chinnapu G. Reddy A. S. Kanagasabapathy Pragna Rao 《Indian journal of clinical biochemistry : IJCB》2005,20(2):146-149
Accurate monitoring of blood cyclosporin C2 levels is vital to prevent over immunosuppression and acute renal toxicity in
patients who receive organ transplant. The matrix used to dilute patients’ C2 samples prior to the assay affected the final
measured values. Hence there was a need to develop a method of dilution that would accurately estimate C2 levels when cyclosporin
levels were beyond the calibration range of the method employed. Whole blood, cyclosporin free hemolysate and cell and protein
free supernatant obtained after pretreatment of normal blood were used to dilute patients’ C2 samples. C2 was measured in
188 patients using the supernatant method of dilution. C2 was correlated with Co and dose of cyclosporin received by the patient.
The use of cell and protein free supernatant obtained after pretreatment of normal blood as a C2 diluent detected higher levels
of C2 in the sample. Measured C2 correlated significantly with Co and the cyclosporin dose received by the patient. The uniformly
aqueous cell and protein free supernatant ensures uniform dilution of the patients’ C2 sample and measures higher cyclosporin
levels. 相似文献