全文获取类型
收费全文 | 11862篇 |
免费 | 957篇 |
国内免费 | 785篇 |
出版年
2024年 | 21篇 |
2023年 | 216篇 |
2022年 | 413篇 |
2021年 | 666篇 |
2020年 | 422篇 |
2019年 | 539篇 |
2018年 | 555篇 |
2017年 | 357篇 |
2016年 | 518篇 |
2015年 | 739篇 |
2014年 | 832篇 |
2013年 | 964篇 |
2012年 | 1113篇 |
2011年 | 976篇 |
2010年 | 600篇 |
2009年 | 515篇 |
2008年 | 563篇 |
2007年 | 517篇 |
2006年 | 451篇 |
2005年 | 378篇 |
2004年 | 320篇 |
2003年 | 241篇 |
2002年 | 197篇 |
2001年 | 203篇 |
2000年 | 172篇 |
1999年 | 181篇 |
1998年 | 106篇 |
1997年 | 131篇 |
1996年 | 110篇 |
1995年 | 91篇 |
1994年 | 95篇 |
1993年 | 48篇 |
1992年 | 74篇 |
1991年 | 55篇 |
1990年 | 44篇 |
1989年 | 47篇 |
1988年 | 38篇 |
1987年 | 27篇 |
1986年 | 19篇 |
1985年 | 22篇 |
1984年 | 12篇 |
1983年 | 9篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1979年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 17 毫秒
991.
Chaofan Li Chi Zhang Geping Luo Xi Chen Bagila Maisupova Abdullo A. Madaminov Qifei Han Bekmamat M. Djenbaev 《Global Change Biology》2015,21(5):1951-1967
Central Asia has a land area of 5.6 × 106 km2 and contains 80–90% of the world's temperate deserts. Yet it is one of the least characterized areas in the estimation of the global carbon (C) stock/balance. This study assessed the sizes and spatiotemporal patterns of C pools in Central Asia using both inventory (based on 353 biomass and 284 soil samples) and process‐based modeling approaches. The results showed that the C stock in Central Asia was 31.34–34.16 Pg in the top 1‐m soil with another 10.42–11.43 Pg stored in deep soil (1–3 m) of the temperate deserts. They amounted to 18–24% of the global C stock in deserts and dry shrublands. The C stock was comparable to that of the neighboring regions in Eurasia or major drylands around the world (e.g. Australia). However, 90% of Central Asia C pool was stored in soil, and the fraction was much higher than in other regions. Compared to hot deserts of the world, the temperate deserts in Central Asia had relatively high soil organic carbon density. The C stock in Central Asia is under threat from dramatic climate change. During a decadal drought between 1998 and 2008, which was possibly related to protracted La Niña episodes, the dryland lost approximately 0.46 Pg C from 1979 to 2011. The largest C losses were found in northern Kazakhstan, where annual precipitation declined at a rate of 90 mm decade?1. The regional C dynamics were mainly determined by changes in the vegetation C pool, and the SOC pool was stable due to the balance between reduced plant‐derived C influx and inhibited respiration. 相似文献
992.
Response of wheat growth,grain yield and water use to elevated CO2 under a Free‐Air CO2 Enrichment (FACE) experiment and modelling in a semi‐arid environment 下载免费PDF全文
Garry J. O'Leary Brendan Christy James Nuttall Neil Huth Davide Cammarano Claudio Stöckle Bruno Basso Iurii Shcherbak Glenn Fitzgerald Qunying Luo Immaculada Farre‐Codina Jairo Palta Senthold Asseng 《Global Change Biology》2015,21(7):2670-2686
The response of wheat crops to elevated CO2 (eCO2) was measured and modelled with the Australian Grains Free‐Air CO2 Enrichment experiment, located at Horsham, Australia. Treatments included CO2 by water, N and temperature. The location represents a semi‐arid environment with a seasonal VPD of around 0.5 kPa. Over 3 years, the observed mean biomass at anthesis and grain yield ranged from 4200 to 10 200 kg ha?1 and 1600 to 3900 kg ha?1, respectively, over various sowing times and irrigation regimes. The mean observed response to daytime eCO2 (from 365 to 550 μmol mol?1 CO2) was relatively consistent for biomass at stem elongation and at anthesis and LAI at anthesis and grain yield with 21%, 23%, 21% and 26%, respectively. Seasonal water use was decreased from 320 to 301 mm (P = 0.10) by eCO2, increasing water use efficiency for biomass and yield, 36% and 31%, respectively. The performance of six models (APSIM‐Wheat, APSIM‐Nwheat, CAT‐Wheat, CROPSYST, OLEARY‐CONNOR and SALUS) in simulating crop responses to eCO2 was similar and within or close to the experimental error for accumulated biomass, yield and water use response, despite some variations in early growth and LAI. The primary mechanism of biomass accumulation via radiation use efficiency (RUE) or transpiration efficiency (TE) was not critical to define the overall response to eCO2. However, under irrigation, the effect of late sowing on response to eCO2 to biomass accumulation at DC65 was substantial in the observed data (~40%), but the simulated response was smaller, ranging from 17% to 28%. Simulated response from all six models under no water or nitrogen stress showed similar response to eCO2 under irrigation, but the differences compared to the dryland treatment were small. Further experimental work on the interactive effects of eCO2, water and temperature is required to resolve these model discrepancies. 相似文献
993.
Xiangguo Wang Pengfei Lin Yanlong Yin Jinhua Zhou Lanjie Lei Xudong Zhou Yaping Jin Aihua Wang 《Cell stress & chaperones》2015,20(3):399-409
Brucella, which is regarded as an intracellular pathogen responsible for a zoonotic disease called brucellosis, survives and proliferates within several types of phagocytic and non-phagocytic cells. Brucella infects not only their preferred hosts but also other domestic and wild animal species, inducing abortion and infertility. Therefore, the interaction between uterine cells and Brucella is important for understanding the pathogenesis of this disease. In this study, we describe the Brucella suis vaccine strain S2 (B.suis.S2) infection and replication in the immortalized caprine endometrial epithelial cell line hTERT-EECs and the induced cellular and molecular response modulation in vitro. We found that B.suis S2 was able to infect and replicate to high titers and inhibit the proliferation of EECs and induce non-apoptotic pathways, as determined by B.suis.S2 detection using MTT and acridine orange/ethidium bromide (AO/EB) staining and flow cytometry. We explored the evidence of non-apoptotic pathways using real-time quantitative RT-PCR and by western blot analysis. Finally, we discovered the over-expression of GRP78, ATF4, ATF6, PERK, eIF2α, CHOP, and cytochrome c (Cyt-c) but not IRE1, xbp-1, and caspase-3 in B.suis.S2 (HK)-attacked and B.suis.S2-infected cells, suggesting that the molecular mechanism of ER stress sensor activation by B.suis.S2 is basically concomitant with that by B.suis.S2 (HK) and that ER stress, especially the PERK pathway, plays an important role in the process of B.suis.S2 infecting EEC, which may, in part, explain the role of the uterus in the pathogenesis of B.suis.S2.
Electronic supplementary material
The online version of this article (doi:10.1007/s12192-014-0564-x) contains supplementary material, which is available to authorized users. 相似文献994.
Joshua D. Campbell Gang Liu Lingqi Luo Ji Xiao Joseph Gerrein Brenda Juan-Guardela John Tedrow Yuriy O. Alekseyev Ivana V. Yang Mick Correll Mark Geraci John Quackenbush Frank Sciurba David A. Schwartz Naftali Kaminski W. Evan Johnson Stefano Monti Avrum Spira Jennifer Beane Marc E. Lenburg 《RNA (New York, N.Y.)》2015,21(2):164-171
995.
Kees Jan van Groenigen Jianyang Xia Craig W. Osenberg Yiqi Luo Bruce A. Hungate 《Global Change Biology》2015,21(12):4293-4297
Elevated atmospheric CO2 concentrations increase plant productivity and affect soil microbial communities, with possible consequences for the turnover rate of soil carbon (C) pools and feedbacks to the atmosphere. In a previous analysis (Van Groenigen et al., 2014), we used experimental data to inform a one‐pool model and showed that elevated CO2 increases the decomposition rate of soil organic C, negating the storage potential of soil. However, a two‐pool soil model can potentially explain patterns of soil C dynamics without invoking effects of CO2 on decomposition rates. To address this issue, we refit our data to a two‐pool soil C model. We found that CO2 enrichment increases decomposition rates of both fast and slow C pools. In addition, elevated CO2 decreased the carbon use efficiency of soil microbes (CUE), thereby further reducing soil C storage. These findings are consistent with numerous empirical studies and corroborate the results from our previous analysis. To facilitate understanding of C dynamics, we suggest that empirical and theoretical studies incorporate multiple soil C pools with potentially variable decomposition rates. 相似文献
996.
997.
998.
999.
1000.
Temporal increases of tree mortality have been observed in regions where global warming has decreased long‐term water availability and/or induced droughts. However, temporal decreases in water availability are not a global phenomenon. Understanding how water deficit‐free forests respond to the recent effects of climate change is paramount towards a full appreciation of the impacts of climate change on global forests. Here, we reveal temporally increasing tree mortality across all study species over the last three decades in the central boreal forests of Canada, where long‐term water availability has increased without apparent climate change‐associated drought. In addition, we find that the effects of conspecific tree‐to‐tree competition have intensified temporally as a mechanism for the increased mortality of shade‐intolerant tree species. Our results suggest that the consequences of climate change on tree mortality are more profound than previously thought. 相似文献