全文获取类型
收费全文 | 6310篇 |
免费 | 460篇 |
国内免费 | 5篇 |
出版年
2023年 | 55篇 |
2022年 | 157篇 |
2021年 | 218篇 |
2020年 | 134篇 |
2019年 | 220篇 |
2018年 | 270篇 |
2017年 | 203篇 |
2016年 | 250篇 |
2015年 | 310篇 |
2014年 | 329篇 |
2013年 | 482篇 |
2012年 | 453篇 |
2011年 | 485篇 |
2010年 | 324篇 |
2009年 | 273篇 |
2008年 | 283篇 |
2007年 | 292篇 |
2006年 | 210篇 |
2005年 | 201篇 |
2004年 | 185篇 |
2003年 | 161篇 |
2002年 | 140篇 |
2001年 | 98篇 |
2000年 | 119篇 |
1999年 | 83篇 |
1998年 | 64篇 |
1997年 | 32篇 |
1996年 | 43篇 |
1995年 | 29篇 |
1994年 | 19篇 |
1993年 | 20篇 |
1992年 | 29篇 |
1991年 | 22篇 |
1990年 | 25篇 |
1989年 | 29篇 |
1988年 | 22篇 |
1987年 | 23篇 |
1986年 | 29篇 |
1985年 | 25篇 |
1984年 | 34篇 |
1983年 | 27篇 |
1982年 | 27篇 |
1981年 | 19篇 |
1980年 | 39篇 |
1979年 | 34篇 |
1978年 | 32篇 |
1977年 | 30篇 |
1976年 | 17篇 |
1974年 | 17篇 |
1973年 | 17篇 |
排序方式: 共有6775条查询结果,搜索用时 15 毫秒
1.
The morphology and innervation of the six oculomotor muscles in the gobiid fishTridentiger trigonocephalus are described. Every rectus muscle is composed of two types of muscle fibres. Muscles attach onto the cartilaginous or fibrous
sclerotica. Oblique muscles attach onto the ethmoidal plate; recti muscles attach onto the parasphenoid or a thick fibrous
membrane. There is no myodome. The common oculomotor nerve is composed of four bundles, the trochlear and the externus of
two. The two kinds of fibres of the lateral rectus and the two distinct bundles of the nerve VI suggest a possible homology
between this muscle in fishes and the lateral rectus+retractor bulbi in mammals. 相似文献
2.
Pierre Beuchet Laïla El kihel Michel Dherbomez Georges Charles Yves Letourneux 《Bioorganic & medicinal chemistry letters》1998,8(24):931
Δ7-5-Desaturase catalyses one of the last steps in ergosterol biosynthesis in fungi. Moreover Δ5-unsaturation is necessary for the sparking function. Synthesis of three pairs of C-6 epimeric cholestanol derivatives are described as potential growth inhibitors. Preliminary results suggest that 6β-aminocholestanol is a potent antifungal agent. 相似文献
3.
The aim of this investigation was to evaluate the semen quality traits of purebred male rabbits and their crosses under subtropical Egyptian conditions. A full 3 x 3 diallel crossing was performed for producing the first generation progeny of New Zealand White (N), Flander (F) and Rex (R) breeds. The highest ejaculate volume (p< 0.05) and percentage of live sperms (p<0.01) with the lowest percentage of sperm cell morphological abnormalities (p<0.05) had been recorded in the NF bucks. Moreover, they possessed positive estimates of direct heterosis for ejaculate volume, mass motility (Mm), individual motility (Im) and sperm cell concentration (SCC). On the contrary, pH had negative estimates of direct heterosis in all crosses and their reciprocal. Semen pH was negatively correlated with SCC (r = -0.18), Mm (r = -0.13) and Im (r = -0.23). In conclusion, the superiority of crossbreeding was particularly obvious in the New Zealand White x Flander males, which cumulated heterosis and favorable maternal effects of the Flander dams. 相似文献
4.
Camera trapping studies have become increasingly popular to produce population estimates of individually recognisable mammals. Yet, monitoring techniques for rare species which occur at extremely low densities are lacking. Additionally, species which have unpredictable movements may make obtaining reliable population estimates challenging due to low detectability. Our study explores the effectiveness of intensive camera trapping for estimating cheetah (Acinonyx jubatus) numbers. Using both a more traditional, systematic grid approach and pre-determined, targeted sites for camera placement, the cheetah population of the Northern Tuli Game Reserve, Botswana was sampled between December 2012 and October 2013. Placement of cameras in a regular grid pattern yielded very few (n = 9) cheetah images and these were insufficient to estimate cheetah density. However, pre-selected cheetah scent-marking posts provided 53 images of seven adult cheetahs (0.61 ± 0.18 cheetahs/100km²). While increasing the length of the camera trapping survey from 90 to 130 days increased the total number of cheetah images obtained (from 53 to 200), no new individuals were recorded and the estimated population density remained stable. Thus, our study demonstrates that targeted camera placement (irrespective of survey duration) is necessary for reliably assessing cheetah densities where populations are naturally very low or dominated by transient individuals. Significantly our approach can easily be applied to other rare predator species. 相似文献
5.
Mingyue Wang Pranab K Mukherjee Jyotsna Chandra Ali Abdul Lattif Thomas S McCormick Mahmoud A Ghannoum 《BMC microbiology》2008,8(1):31
Background
We have previously shown that supernatant from Candida albicans (CA) culture contains a Secretory Interleukin (IL)-12 Inhibitory Factor (CA-SIIF), which inhibits IL-12 production by human monocytes. However, the effect of CA-SIIF on secretion of other cytokines by monocytes is unknown, and detailed characterization of this factor has not been performed. 相似文献6.
7.
8.
9.
Mangoes (Mangifera indica) are grown in many warm regions of the world; for example, in Australia, Brazil, India, South America, and the United States (California and Florida), and along the shores of the Mediterranean sea (Egypt, Italy, and Spain). In Egypt, many varieties yielding delicious fruits are grown in large quantities (50,000 tons annually). Mango kernels are used for feeding mammals and chickens. Starch has been isolated from mango and its physical properties studied.The aim of the present work was to study the polysaccharides present in mango kernels. 相似文献
10.
Summary The influence of total nitrification to nitrate or partial nitrification to nitrite on the soil organic nitrogen status was examined. NH
4
+
–15N was added to the soil in the absence and the presence of NaClO3, respectively nitrapyrin. The first chemical inhibits only nitrate formation, the second inhibits total nitrification. The accumulation of nitrite nitrogen in the soil at levels up to 5 mg kg–1 increased the loss of nitrogen. Yet, it did not increase the binding of mineral nitrogen into soil organic matter, relative to the control soil. The data suggest that the biochemistry of the nitrite formation process, rather than the levels of nitrite ions formed, are of primary importance in the role of nitrification mediated nitrosation of soil organic matter. 相似文献