全文获取类型
收费全文 | 1318篇 |
免费 | 5篇 |
国内免费 | 70篇 |
专业分类
教育 | 929篇 |
科学研究 | 236篇 |
各国文化 | 2篇 |
体育 | 47篇 |
综合类 | 24篇 |
文化理论 | 11篇 |
信息传播 | 144篇 |
出版年
2024年 | 3篇 |
2023年 | 16篇 |
2022年 | 22篇 |
2021年 | 20篇 |
2020年 | 11篇 |
2019年 | 10篇 |
2018年 | 14篇 |
2017年 | 6篇 |
2016年 | 15篇 |
2015年 | 18篇 |
2014年 | 98篇 |
2013年 | 44篇 |
2012年 | 45篇 |
2011年 | 75篇 |
2010年 | 51篇 |
2009年 | 43篇 |
2008年 | 79篇 |
2007年 | 73篇 |
2006年 | 64篇 |
2005年 | 63篇 |
2004年 | 56篇 |
2003年 | 78篇 |
2002年 | 48篇 |
2001年 | 56篇 |
2000年 | 45篇 |
1999年 | 26篇 |
1998年 | 39篇 |
1997年 | 31篇 |
1996年 | 26篇 |
1995年 | 31篇 |
1994年 | 20篇 |
1993年 | 17篇 |
1992年 | 21篇 |
1991年 | 17篇 |
1990年 | 15篇 |
1989年 | 11篇 |
1988年 | 8篇 |
1987年 | 12篇 |
1986年 | 12篇 |
1985年 | 3篇 |
1984年 | 7篇 |
1983年 | 6篇 |
1982年 | 5篇 |
1981年 | 7篇 |
1980年 | 4篇 |
1978年 | 2篇 |
1963年 | 2篇 |
1959年 | 4篇 |
1956年 | 2篇 |
1951年 | 1篇 |
排序方式: 共有1393条查询结果,搜索用时 15 毫秒
11.
12.
13.
在PH2.0-4.0的介质中Fe(Ⅲ)能协同过氧化氢氧化I^-析出I2,提出了在酸性条件下I^- -Fe(Ⅲ)-H2O2-淀粉体系用四氯化碳萃取光度法测定微量碘的方法,和I^- -Fe(Ⅲ)-H2O2-体系的四氯化碳萃取光度法测定微量碘相比较,灵敏度分别提高了1.4倍与3.2倍,该方法具有萃取时间短之特点,且用于食盐中微量的测定,结果令人满意。 相似文献
14.
从传统建筑色彩的起源、发展历程入手,总结中国传统建筑的设色规律.并进一步总结传统建筑色彩反映的深刻的文化理念,包括与五行学说的联系,以及封建等级思想对色彩美学发展的影响.最后,试着探讨传统建筑色彩美学在现代建筑设计中的应用方式,并举例加以论证. 相似文献
15.
The present paper deals with the genus Paeonia in Xinjiang, whose taxonomy has
been confused. Based on the field observation, population sampling and the examination of
herbarium specimens, a taxonomical revision is made in this paper. Two species are recog-
nized, i. e. Paeonia anomala L. and P. sinjiangensis K. Y. Pan. P. altaica K. M. Dai
et T. H. Ying is reduced to P. sinjiangensis and P. hybrida (= P. anomala var.
intermedia) is reduced to P. anomala. The diagnostic characters of the two species are de-
scribed and illustrated, and a map of their distribution in Xinjiang is presented. A key to
these two species is provided here.
1. Roots straight, not thickened; sepals all caudate, less frequently one or very rarely two
non-caudate ................................................ 1. P. sinjiangensis K. Y. Pan.
2. Roots fusiform or tuberous; inner three sepals non-caudate, less frequently one of them
caudate .............................................................. 2. P. anomala L.
key words Xinjiang; Paeonia; P. anomala; P. sinjiangensis; revision 相似文献
16.
本文根据作者等10多年来对广西杉木林生产力测定数据和与之相匹配的年平均气温、温暖指数、降水量、温度指数和实际蒸散量等气象数据,用最小二乘法建立了杉木林的气候生产力模型,给出了全区杉木林气候生产力分布,并与迈阿密和桑斯威特数学模型的计算结果做了比较分析。结果杉木林、气候生产力、模型、广西 相似文献
17.
光学显微镜和扫描电镜观察表明,金钱豹属(广义)花粉明显分为两个类型:Campanumoea inflata和C.javanica subsp.laponica的花粉5~8沟,外壁具相对密的短刺,刺高不过1μm,而C.lancifolia,C.celebica和C.parviflora的花粉3孔沟,外壁刺稀疏,高于2μm。种子表面纹饰也同样可分为 两类,前两个种一类,其种子表面网状,网眼规则而多角形,直径大于网脊宽度,网脊上的次级纹饰为念 珠状,而后三种为一类,其种子表面网眼不规则,直径与网脊宽度近相等,网脊上的次级纹饰绳索状。可 见花粉特征与种皮性状是高度相关的。后三个种所属的分类群就是被归并了的属Cyclocodon Griffith。 综合花粉、种皮及外部形态,这个属应予恢复。其近缘属应是Platycodon,而不是Campanumoea。 相似文献
18.
芍药属的研究(1)——国产几个野生种核型的报道 总被引:1,自引:0,他引:1
In the present paper 8 species with 15 populations of the genus Paeonia L. (if P.
papaveracea and P. japonica are recognised as species) were collected from Sichuan, Shaanxi
and Hebei provinces (see the Appendix for detail of the materials). The micrographs of their
somatic metaphase (also Mii in the case of P.veitchii) are shown in Plates 1-4, the karyo-
type formulae, ranges of chromosome length and classification of karyotypes according to Steb-
bins (1971) are shown in Table 5: the idiograms in Figs. 1-2, and the parameters of chromo-
somes in Table 1-4. The essential points are mentioned as follows:
(1) Chromosomes of the various species in the section Modan have so far been examined
and they are all diploid, the two species in the section Onaepia are also diploid, and thus
tetraploids exist only in the section Paeonia.
(2) Chromosomes in the genus Paeonia are relatively stable except for the differentiation
of ploidy. The karyotypes (Table 1-4) show no differences among different taxa in Sect.
Modan and the same can also be said about the taxa in Sect. Paeonia (Table 1). Not only
are the karyotypes very similar, but also among the members within either section have the
same parameters of chromosomes, and, differences, if occur, are not statistically significant.
Between the two sections, however, the situation is different. The arm ratios of the first pairs of
chromosomes in Sect. Modan are 1.53, 1.52 and 1.48 (Table 1), but those in Sect. Paeonia
are 1.12-1.28 (Table 2-4), 95% confidence limits are 1.46-1.60 for the section Modan and
1.07-1.28 (1.21-1.35 only for PB85078) for the section Paeonia, not overlapping, which indi-
cates that the two sections have differentiated in respect of the first pairs of chromosomes.
(3)The population PB85024, which belongs to the P. obovata complex, has a karyotype of
2B (stebbins, 1971), which is a new one in the genus Paeonia. This karyotype is a stable one,
for several individuals in the population are uniform in this respect, which shows that Steb-
bins’ (1971) generalization that all the species in Paeonia have 2A does not hold true.
(4) Three populations of P. obovata complex studied in this work from Sichuan and
Shaanxi are all tetraploids, and one from Hebei is a diploid. From the present work and
the previcus reports, the materials from Japan and Korea, no matter whether flowers are pink
or white, are diploids, those from Heilongjiang Province (with both pink and white flowers)
(Liu Ming-yuan, personal communication) and from Heibei Province (with pink flowers)
in China are also diploids, the one from Sakhalin (pink flowers) is tetraploid, those from
Priamur of the Soviet Union are a tetraploid (with white flowers) and a diploid (with pink
flowers), and those from Shaanxi (the Qinling Range) and western Sichuan (with both pink
and white flowers) are all tetraploids. As far as we have now known, ploidy in this parti-
cular complex is correlated with the geographical distribution: diploids are found in the cen-
tral part, tetraploids occur in the northern limits, and in the south letraploids are the only
cytotype.
(5) The materials of P. mairei from western Sichuan and Shaanxi (the Qinling Range)
are found all to be tetraploids, which shows that two cytotypes, diploid and tetraploid, exist in
this species, but the geographical distribution pattern of these two cytotypes is to be revealed
in the future investigation. 相似文献
19.
本文报道浙江产菝葜属smilax 7个种的染色体数目和核型。S.nipponica有两种核型,2n=
26和2n=32,均为3B型,但后一种细胞型的雄株的第一对染色体大小不等,可能为性染色体;S.
riparia 2n=30,属3B型;S.siebodii n=16;S. china有两个染色体数目,2n=96 和n=15;
S. davidiana 2n=32,属3B型,对减数分裂MI的观察发现n=16;S.glabra 2n=32,亦属3B
型:S. nervo-marginata var.liukiuensis 2n=32,属3C型。讨论了种间在核型上的差异、属的基数、
核型演化趋势和性染色体等问题。 相似文献
20.
近几年来,我国的公路交通事业得到快速发展,特别是高速公路的建设,速度更是惊人。1995年全国公路总里程为115.7万km,到2004年末已达到190万km,高速公路总里程也已超过3万公里。但在公路交通快速发展的同时也带来了日益严重的环境问题。其中水土流失、生物多样性减少等公路建设过程的生态环境问题以及公路交通噪声、汽车废气、水质污染等环境质量问题已为人们日益关注。在这里我就公路工程中常用的水土保持措施方法和大家一同探讨,希望大家能提出宝贵的意见和建议。1,公路工程中常用的坡面防护措施公路工程中常用的坡面防护措施有以下几种类… 相似文献