全文获取类型
收费全文 | 27206篇 |
免费 | 3016篇 |
国内免费 | 9697篇 |
出版年
2024年 | 207篇 |
2023年 | 713篇 |
2022年 | 1149篇 |
2021年 | 1487篇 |
2020年 | 1230篇 |
2019年 | 1420篇 |
2018年 | 1083篇 |
2017年 | 1026篇 |
2016年 | 1237篇 |
2015年 | 1791篇 |
2014年 | 2225篇 |
2013年 | 2142篇 |
2012年 | 2755篇 |
2011年 | 2662篇 |
2010年 | 1941篇 |
2009年 | 2002篇 |
2008年 | 2201篇 |
2007年 | 2045篇 |
2006年 | 1845篇 |
2005年 | 1532篇 |
2004年 | 1192篇 |
2003年 | 1070篇 |
2002年 | 1001篇 |
2001年 | 737篇 |
2000年 | 655篇 |
1999年 | 503篇 |
1998年 | 231篇 |
1997年 | 208篇 |
1996年 | 175篇 |
1995年 | 145篇 |
1994年 | 149篇 |
1993年 | 137篇 |
1992年 | 132篇 |
1991年 | 124篇 |
1990年 | 99篇 |
1989年 | 83篇 |
1988年 | 56篇 |
1987年 | 44篇 |
1986年 | 58篇 |
1985年 | 61篇 |
1984年 | 46篇 |
1983年 | 24篇 |
1982年 | 50篇 |
1981年 | 23篇 |
1980年 | 21篇 |
1978年 | 14篇 |
1977年 | 17篇 |
1976年 | 17篇 |
1975年 | 14篇 |
1974年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
Rong Ge Honglin He Xiaoli Ren Li Zhang Guirui Yu T. Luke Smallman Tao Zhou Shi‐Yong Yu Yiqi Luo Zongqiang Xie Silong Wang Huimin Wang Guoyi Zhou Qibin Zhang Anzhi Wang Zexin Fan Yiping Zhang Weijun Shen Huajun Yin Luxiang Lin 《Global Change Biology》2019,25(3):938-953
It is critical to accurately estimate carbon (C) turnover time as it dominates the uncertainty in ecosystem C sinks and their response to future climate change. In the absence of direct observations of ecosystem C losses, C turnover times are commonly estimated under the steady state assumption (SSA), which has been applied across a large range of temporal and spatial scales including many at which the validity of the assumption is likely to be violated. However, the errors associated with improperly applying SSA to estimate C turnover time and its covariance with climate as well as ecosystem C sequestrations have yet to be fully quantified. Here, we developed a novel model‐data fusion framework and systematically analyzed the SSA‐induced biases using time‐series data collected from 10 permanent forest plots in the eastern China monsoon region. The results showed that (a) the SSA significantly underestimated mean turnover times (MTTs) by 29%, thereby leading to a 4.83‐fold underestimation of the net ecosystem productivity (NEP) in these forest ecosystems, a major C sink globally; (b) the SSA‐induced bias in MTT and NEP correlates negatively with forest age, which provides a significant caveat for applying the SSA to young‐aged ecosystems; and (c) the sensitivity of MTT to temperature and precipitation was 22% and 42% lower, respectively, under the SSA. Thus, under the expected climate change, spatiotemporal changes in MTT are likely to be underestimated, thereby resulting in large errors in the variability of predicted global NEP. With the development of observation technology and the accumulation of spatiotemporal data, we suggest estimating MTTs at the disequilibrium state via long‐term data assimilation, thereby effectively reducing the uncertainty in ecosystem C sequestration estimations and providing a better understanding of regional or global C cycle dynamics and C‐climate feedback. 相似文献
992.
993.
Click reactions between alkynes and azides using the privileged scaffold of triterpenes have been of interest for biological chemistry. Many publications deal with the synthesis of novel bioactive molecules; these conjugates have also been used for bioanalytical and diagnostic purposes. As a result, conjugates of better physicochemical properties were obtained; even compounds of improved solubility in water and physiological fluids were made through the introduction of a triazol residue. “Hybrid-structures“, i.e. molecules consisting of two independently bioactive subunits linked by a triazole residue were higher bioactive than their parent compounds but not as active as expected, and with a few exceptions the ultimate breakthrough has not yet been achieved. Only in the synthesis of compounds with anti-leishmanial activity some new and promising lead structures were found. As a consequence, triazole modified triterpenes seem to hold their greatest future prospect rather as diagnostic reagents and molecular probes than as drugs. 相似文献
994.
Ping Yu Wenjing Liu Jinghui Ren Yingying Wang Yao Ning Mingqi Huang Xinyi Hu Lili Wei Min Ji Jin Cai 《Bioorganic & medicinal chemistry letters》2019,29(16):2168-2172
Bromodomain-containing protein 4 (BRD4) is a new therapeutic target for the treatment of diseases including cardiovascular diseases, cancer, inflammation and central nervous system (CNS) disorders. In this study, we introduced the pharmacophore of fibrates to a BRD4 inhibitor, RVX-208, to design dual-active hypolipidemic compounds, and found that some of new analogues showed favorable hypolipidemic activities. Synthetic accessibility towards this class of compounds optimized RVX-208 as well as would supply more thoughts on hypolipidemic drugs. 相似文献
995.
996.
Synthesis and biological evaluation of BMS-986120 and its deuterated derivatives as PAR4 antagonists
Panpan Chen Shenhong Ren Hangyu Song Cai Chen Fangjun Chen Qinglong Xu Yi Kong Hongbin Sun 《Bioorganic & medicinal chemistry》2019,27(1):116-124
BMS-986120 is a PAR4 antagonist that is being investigated as an antiplatelet agent in phase I clinical trial. An improved synthesis of BMS-986120 has been developed. Based on the novel synthetic approach to BMS-986120, a series of deuterated derivatives of BMS-986120 have been synthesized and biologically evaluated to search for more potent antiplatelet agents. The in vitro antiplatelet assay by turbidimetry demonstrated that PC-2 and PC-6 had IC50 values of 6.30?nM and 6.97?nM, respectively, versus BMS-986120 with an IC50 of 7.80?nM. The result of in vitro metabolic stability study showed that all of the deuterated compounds had similar half-life (T1/2) and intrinsic clearance (Clint) in comparison with BMS-986120. Further probing the metabolic profile of BMS-986120 is worth being conducted. 相似文献
997.
Shan Xiao Lin Wei Zongqin Hong Li Rao Yanliang Ren Jian Wan Lingling Feng 《Bioorganic & medicinal chemistry》2019,27(5):805-812
By using a new Fragment-Based Virtual Screen strategy, two series of novel FBA-II inhibitors (thiourea derivatives) were de novo discovered based on the active site of fructose-1, 6-bisphosphate aldolase from Cyanobacterial (CyFBA). In comparison, most of the N-(2-benzoylhydrazine-1-carbonothioyl) benzamide derivatives (L14~L22) exhibit higher CyFBA-II inhibitory activities compared to N-(phenylcarbamothioyl) benzamide derivatives (L1~L13). Especially, compound L14 not only shows higher CyFBA-II activity (Ki?=?0.65?μM), but also exhibits most potent in vivo activity against Synechocystis sp. PCC 6803 (EC50?=?0.09?ppm), higher (7-fold) than that of our previous inhibitor (EC50?=?0.6?ppm). The binding modes of compound L14 and CyFBA-II were further elucidated by jointly using DOX computational protocol, MM-PBSA and site-directed mutagenesis assays. The positive results suggest that strategy adopted in this study was promising to rapidly discovery the potent inhibitors with novel scaffolds. The satisfactory algicide activities suggest that the thiourea derivatives is very likely to be a promising lead for the development of novel specific algicides to solve Cyanobacterial harmful algal blooms (CHABs). 相似文献
998.
999.
1000.
Yun Ren Dan Chen Wenjie Li Dan Zhou Tao Luo Guoqiang Yuan Jing Zeng Ye Cao Zhongshan He Ting Zou Qiming Deng Shiquan Wang Aiping Zheng Jun Zhu Yueyang Liang Huainian Liu Lingxia Wang Ping Li Shuangcheng Li 《The Plant journal : for cell and molecular biology》2019,98(2):315-328
Meiosis is essential for eukaryotic sexual reproduction and plant fertility, and crossovers (COs) are essential for meiosis and the formation of new allelic combinations in gametes. In this study, we report the isolation of a meiotic gene, OsSHOC1, and the identification of its partner, OsPTD1. Osshoc1 was sterile both in male and female gametophytes, and it showed a striking reduction in the number of meiotic COs, indicating that OsSHOC1 was required for normal CO formation. Further investigations showed that OsSHOC1 physically interacted with OsPTD1 and that the latter was also required for normal CO formation and plant fertility. Additionally, the expression profiles of both genes were consistent with their functions. Our results suggest that OsSHOC1 and OsPTD1 are essential for rice fertility and CO formation, possibly by stabilizing the recombinant intermediates during meiosis. 相似文献