全文获取类型
收费全文 | 25248篇 |
免费 | 395篇 |
国内免费 | 16篇 |
专业分类
教育 | 18262篇 |
科学研究 | 2068篇 |
各国文化 | 258篇 |
体育 | 1971篇 |
综合类 | 14篇 |
文化理论 | 182篇 |
信息传播 | 2904篇 |
出版年
2022年 | 188篇 |
2021年 | 289篇 |
2020年 | 417篇 |
2019年 | 653篇 |
2018年 | 898篇 |
2017年 | 886篇 |
2016年 | 785篇 |
2015年 | 487篇 |
2014年 | 743篇 |
2013年 | 4943篇 |
2012年 | 709篇 |
2011年 | 713篇 |
2010年 | 525篇 |
2009年 | 561篇 |
2008年 | 634篇 |
2007年 | 545篇 |
2006年 | 473篇 |
2005年 | 472篇 |
2004年 | 434篇 |
2003年 | 402篇 |
2002年 | 385篇 |
2001年 | 515篇 |
2000年 | 439篇 |
1999年 | 405篇 |
1998年 | 238篇 |
1997年 | 243篇 |
1996年 | 283篇 |
1995年 | 262篇 |
1994年 | 217篇 |
1993年 | 227篇 |
1992年 | 355篇 |
1991年 | 326篇 |
1990年 | 319篇 |
1989年 | 310篇 |
1988年 | 272篇 |
1987年 | 312篇 |
1986年 | 282篇 |
1985年 | 321篇 |
1984年 | 261篇 |
1983年 | 229篇 |
1982年 | 202篇 |
1981年 | 177篇 |
1980年 | 164篇 |
1979年 | 267篇 |
1978年 | 193篇 |
1977年 | 173篇 |
1976年 | 163篇 |
1975年 | 151篇 |
1974年 | 155篇 |
1971年 | 141篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
111.
112.
Quantum chemistry is based on the solution of the Schrödinger equation for a molecule. From starting data on the positions and nature of constituent atoms information is provided about the energy of the molecule and its electronic properties. The former can indicate what shapes drugs can adopt in binding to pharmacological receptors whilst electronic details, when compared using computer graphics, may highlight the factors responsible for biological activity. These techniques are beginning to show real successes in the design of drug molecules. 相似文献
113.
114.
F. M. Reza 《Journal of The Franklin Institute》1985,320(6)
The normal family of linear (time-variant) n-ports is introduced as the most natural extension of ordinary scalar driving-point immittance behaviour. The normality induces a certain symmetry and simplicity which merits due emphasis in future n-port research investigations. As an application of the concept of normality the overdamped-underdamped criterion is extended to n-ports. Also, an interesting problem of maximal power transfer is solved and the absolute energy invariant index calculated. This paper invites attention to the development of circuit synthesis procedures based on the algebraic structure of the normal family. 相似文献
115.
Knight DM 《Endeavour》2000,24(4):165-169
Humphry Davy (1778–1829) was one of the first professional scientists, earning his living and rising spectacularly from an impoverished upbringing in Cornwall to be President of the Royal Society and a baronet. He owed his rise to patronage as well as to his range of abilities: as a lecturer, as a chemical theorist and as a very early applied scientist. But his exalted position brought him little happiness, for he could not satisfy all the hopes put upon him as the successor to Sir Joseph Banks. Admired rather than loved, he became unpopular and was seen as haughty. In his last two years, spent wandering lonely and sickly in Italy and the Alps, he sought to make sense of his life, writing dialogues as his bequest to the new generation. 相似文献
116.
P. Sharma M. Bose Isa Mohd S. Bagdi H. G. Raj 《Indian journal of clinical biochemistry : IJCB》2000,15(2):83-87
Genomic DNA from a clinical isolate ofMycobacterium avium-intracellulare complex was purified and cloned in PBR 322 at the tetracycline resistance site using Bam HI restriction enzyme. A 16 kb cloned
fragment was purified, radiolabeled and used as a probe. Genomic DNA isolated from nineteen MAC strains, threeM. tuberculosis strains and oneM. kansasii strain were digested with Eco RI restriction enzyme, Southern blotted and hybridized with the 16 kb cloned and labeled fragment.
Twelve MAC strains showed positive hybridization although five strains gave faint signals. Positive hybridization was noted
in two out of the threeM. tuberculosis strains, possibly due to shared DNA homology. No signal was received from the singleM. kansasii strain used in this study. 相似文献
117.
Soma Gupta K. K. Singh V. J. Vyas V. N. Chaturvedi M. V. R. Reddy B. C. Harinath 《Indian journal of clinical biochemistry : IJCB》2000,15(1):52-55
Oxidative stress was studied by estimating plasma levels of malondialdehyde (MDA), beta carotene, vitamin E and erythrocytic
superoxide dismutase(E-SOD) activity in 50 cases of carcinoma of upper digestive tract which included carcinoma of oral cavity,
pharynx and oesophagus. While plasma MDA level was found to be increased (3.5±1.0 nmole/ml), a significant decrease in beta
carotene (81.2±14.5mg%), vitamin E (8.5±1.1 mg/L) level and E-SOD activity (657.0±80.6 U/G Hb) were observed in carcinoma
of upper digestive tract. Patients were treated with radiotherapy which itself was toxic enough and produced its deleterious
effects by generation of reactive oxygen species (ROS). As antioxdiants can detoxify ROS, beneficial effect if any, of antioxidant
administration during radiotherapy was studied in two groups of patients, group A (n=5, supplemented with antioxidants) and
group B (n=5, without antioxidant supplementation). Plasma MDA level was found to be elevated in both the groups but the increase
in group B was significant, compared to pretreatment level. Further, body weight was found to be significantly decreased in
group B patients, which was maintained in group A patients. Moreover, group A patients showed significant elevation in beta
carotene concentration, thus showing beneficial effect of administration of antioxidants during radiotherapy without disturbing
the desirable therapeutic effect of radiotherapy. 相似文献
118.
Large-scale assessments often use a computer adaptive test (CAT) for selection of items and for scoring respondents. Such tests often assume a parametric form for the relationship between item responses and the underlying construct. Although semi- and nonparametric response functions could be used, there is scant research on their performance in a CAT. In this work, we compare parametric response functions versus those estimated using kernel smoothing and a logistic function of a monotonic polynomial. Monotonic polynomial items can be used with traditional CAT item selection algorithms that use analytical derivatives. We compared these approaches in CAT simulations with a variety of item selection algorithms. Our simulations also varied the features of the calibration and item pool: sample size, the presence of missing data, and the percentage of nonstandard items. In general, the results support the use of semi- and nonparametric item response functions in a CAT. 相似文献
119.
As the American population continues to become more diverse there is a need to provide children in early education with factual information about all ethnic groups to decrease prejudice. First, teachers must examine their own beliefs prior to implementing a multicultural approach into the curriculum. Three questions are presented that will assist teachers in evaluating their views and behaviors toward ethnic groups. Informative resources are provided for teachers to educate themselves, parents, and students. Through children's literature, instructional materials, and Internet sources, teachers can promote more positive attitudes among students and educate children to be respectful and accept the individuality of others. 相似文献
120.