全文获取类型
收费全文 | 28177篇 |
免费 | 2415篇 |
国内免费 | 2568篇 |
出版年
2024年 | 49篇 |
2023年 | 220篇 |
2022年 | 534篇 |
2021年 | 1007篇 |
2020年 | 840篇 |
2019年 | 1014篇 |
2018年 | 1036篇 |
2017年 | 835篇 |
2016年 | 1047篇 |
2015年 | 1632篇 |
2014年 | 2012篇 |
2013年 | 2214篇 |
2012年 | 2703篇 |
2011年 | 2425篇 |
2010年 | 1668篇 |
2009年 | 1445篇 |
2008年 | 1934篇 |
2007年 | 1669篇 |
2006年 | 1531篇 |
2005年 | 1292篇 |
2004年 | 1269篇 |
2003年 | 1129篇 |
2002年 | 1011篇 |
2001年 | 443篇 |
2000年 | 335篇 |
1999年 | 274篇 |
1998年 | 264篇 |
1997年 | 157篇 |
1996年 | 146篇 |
1995年 | 145篇 |
1994年 | 108篇 |
1993年 | 91篇 |
1992年 | 85篇 |
1991年 | 72篇 |
1990年 | 54篇 |
1989年 | 60篇 |
1988年 | 45篇 |
1987年 | 46篇 |
1986年 | 37篇 |
1985年 | 43篇 |
1984年 | 16篇 |
1983年 | 20篇 |
1982年 | 27篇 |
1981年 | 11篇 |
1979年 | 14篇 |
1978年 | 10篇 |
1977年 | 12篇 |
1976年 | 10篇 |
1975年 | 9篇 |
1973年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
881.
Insect distribution in response to climate change based on a model: Review of function and use of CLIMEX 总被引:1,自引:0,他引:1
下载免费PDF全文
![点击此处可从《Entomological Research》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The significant dependence of agricultural productivity on pest control requires pest distribution predictions at an early stage of pest invasion. Because pest cycles are critically affected by climate, climate is one of the most important factors for predicting an invasive pest. CLIMEX is a highly effective tool that can predict potential geographical species distributions, and test the regional suitability for a target species' habitat based on data including climate change scenarios. CLIMEX has been recently used in Europe, North America, China and Australia, among others. However, for modeling species distributions in Korea, the use of the model has been limited to date. This study aimed to first introduce the function and application of CLIMEX by reviewing important studies using this model. Second, we investigated previous studies using the model simulation to demonstrate the practical applicability of CLIMEX for the agricultural sector, and its use in forecasting. 相似文献
882.
Jitsuki?SawamuraEmail author Shigeru?Morishita Jun?Ishigooka 《Theoretical biology & medical modelling》2016,13(1):5
Background
Previously, we applied basic group theory and related concepts to scales of measurement of clinical disease states and clinical findings (including laboratory data). To gain a more concrete comprehension, we here apply the concept of matrix representation, which was not explicitly exploited in our previous work.Methods
Starting with a set of orthonormal vectors, called the basis, an operator Rj (an N-tuple patient disease state at the j-th session) was expressed as a set of stratified vectors representing plural operations on individual components, so as to satisfy the group matrix representation.Results
The stratified vectors containing individual unit operations were combined into one-dimensional square matrices [Rj]s. The [Rj]s meet the matrix representation of a group (ring) as a K-algebra. Using the same-sized matrix of stratified vectors, we can also express changes in the plural set of [Rj]s. The method is demonstrated on simple examples.Conclusions
Despite the incompleteness of our model, the group matrix representation of stratified vectors offers a formal mathematical approach to clinical medicine, aligning it with other branches of natural science.883.
A study was conducted to determine the efficacy of β-mannanase supplementation to a diet based on corn and soya bean meal (SBM) on growth performance, nutrient digestibility, blood urea nitrogen (BUN), faecal coliforms and lactic acid bacteria, and noxious gas emission in growing pigs. A total of 140 pigs [(Landrace × Yorkshire) × Duroc; average body weight 25 ± 3 kg] were randomly allotted to a 2 × 2 factorial arrangement with dietary treatments consisting of hulled or dehulled SBM without or with supplementation of 400 U β-mannanase/kg. During the 6 weeks of experimental feeding, β-mannanase supplementation had no effect on body weight gain, feed intake and gain:feed (G:F) ratio. Compared with dehulled SBM, feeding hulled SBM caused an increased feed intake of pigs in the entire trial (p = 0.05). The G:F ratio was improved in pigs receiving dehulled SBM (p < 0.05). Dietary treatments did not influence the total tract digestibility of dry matter, nitrogen and gross energy. Enzyme supplementation reduced (p < 0.05) the population of faecal coliforms and tended to reduce the NH3 concentration after 24 h of fermentation in a closed box containing faecal slurry. Feeding hulled SBM tended to reduce NH3 emission on days 3 and 5 of fermentation. In conclusion, mannanase supplementation had no influence on growth performance and nutrient digestibility but showed a positive effect on reducing coliform population and tended to reduce NH3 emission. Dehulled SBM increased G:F ratio and hulled SBM tended to reduce NH3 emission. 相似文献
884.
Investigation on the interaction of letrozole with herring sperm DNA through spectroscopic and modeling methods
下载免费PDF全文
![点击此处可从《Luminescence》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Yan‐Mei Huang Shou‐Jun Zheng Jin Yan Hong‐Qin Yang Di Wu Qing Wang Hui Li 《Luminescence》2016,31(5):1077-1084
The interaction of letrozole, an efficient and safe aromatase inhibitor, with herring sperm DNA (hsDNA) was investigated in vitro through spectroscopy analysis and molecular modeling to elucidate the binding mechanism of anticancer drugs and DNA. The binding constant and the number of binding sites were 2.13 × 104 M?1 and 1.09, respectively, at 298 K. Thermodynamic parameters (ΔG, ΔH and ΔS) exhibited negative values, which indicated that binding was spontaneous and Van der Waals forces and hydrogen bond were the main interaction forces. Fourier transform infrared spectroscopy and other spectroscopy analysis methods illustrated that letrozole could intercalate into the phosphate backbone of hsDNA and interact with the nitrogenous bases. Consistent with the experimental findings, molecular modeling results demonstrated that the interaction was dominated by intercalation and hydrogen bonding. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
885.
褐飞虱Nilaparvata lugens Stl是我国重要的迁飞性水稻害虫,本文研究了金龟子绿僵菌Metarhizium anisopliae及其与dsRNA混合使用对褐飞虱的防治效果。绿僵菌悬浮液1.6×108孢子/m L至8×106孢子/m L对褐飞虱2龄、4龄和成虫进行喷药,发现1.6×107孢子/m L对各个虫态虫龄均有良好致死效果,并且成虫和4龄若虫均好于2龄若虫。在交配行为上来看,绿僵菌处理过的褐飞虱成虫活跃度非常低,从配对开始一直到交配结束的各个阶段都受到明显影响,处理组3 h的交配率只有3.70%,而对照组的交配率为24.44%。还把褐飞虱几丁质合成酶基因A的dsRNA与绿僵菌混合使用防治褐飞虱2龄和4龄若虫,结果表明0.5μg/μL ds CHSA与绿僵菌混合使用的防治效果最好,2龄若虫的死亡率为89.63%,4龄若虫的死亡率达到93.94%。而0.2μg/μL ds CHSA与绿僵菌的混合,对2龄和4龄若虫的致死率为65.56%-76.52%。研究结果为褐飞虱的生物防治提供了新的思路。 相似文献
886.
Integrated long non‐coding RNA analyses identify novel regulators of epithelial‐mesenchymal transition in the mouse model of pulmonary fibrosis
下载免费PDF全文
![点击此处可从《Journal of cellular and molecular medicine》网站下载免费的PDF全文](/ch/ext_images/free.gif)
887.
Offshore and coastal common bottlenose dolphins of the western South Atlantic face‐to‐face: What the skull and the spine can tell us
下载免费PDF全文
![点击此处可从《Marine Mammal Science》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Ana P. B. Costa Patricia E. Rosel Fábio G. Daura‐Jorge Paulo C. Simões‐Lopes 《Marine Mammal Science》2016,32(4):1433-1457
The taxonomy of Tursiops truncatus in the western South Atlantic is not resolved. Two different hypotheses have been proposed: (1) offshore and coastal ecotypes with a parapatric distribution, and (2) two species, T. truncatus and T. gephyreus, living in sympatry. To test these hypotheses, we examined a total of 100 physically mature skulls and 35 vertebral columns from the suggested overlap zone in southern Brazil. In all skulls, 24 measurements, four alveoli counts and two categorical variables were analyzed. Vertebral formula was determined and five measurements were taken from selected vertebrae. Multivariate analyses were conducted for skull and vertebral data. Results revealed the presence of two well‐separated groups. Specimens of Group1 had smaller skulls and shorter body lengths, but more vertebrae, than Group2. The morphological characteristics of each group corresponded well with two ecotypes of common bottlenose dolphins reported in other ocean basins. Therefore, we assigned the specimens of Group1 to the offshore ecotype, and Group2 to the coastal ecotype. Differences in the geographic locations and ratio of strandings supported the parapatric hypothesis. The significant morphological differentiation observed suggests the presence of different subspecies, but an additional independent line of evidence is needed to hypothesize whether they represent different species. 相似文献
888.
889.
890.