首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   15034篇
  免费   1540篇
  国内免费   3889篇
  20463篇
  2024年   127篇
  2023年   389篇
  2022年   720篇
  2021年   933篇
  2020年   763篇
  2019年   894篇
  2018年   757篇
  2017年   551篇
  2016年   716篇
  2015年   1044篇
  2014年   1281篇
  2013年   1218篇
  2012年   1511篇
  2011年   1389篇
  2010年   976篇
  2009年   903篇
  2008年   1025篇
  2007年   874篇
  2006年   768篇
  2005年   704篇
  2004年   617篇
  2003年   490篇
  2002年   403篇
  2001年   250篇
  2000年   229篇
  1999年   161篇
  1998年   114篇
  1997年   86篇
  1996年   71篇
  1995年   68篇
  1994年   53篇
  1993年   47篇
  1992年   46篇
  1991年   30篇
  1990年   38篇
  1989年   26篇
  1988年   19篇
  1987年   16篇
  1986年   15篇
  1985年   15篇
  1984年   10篇
  1983年   9篇
  1982年   10篇
  1981年   8篇
  1978年   6篇
  1974年   6篇
  1959年   5篇
  1958年   7篇
  1957年   9篇
  1956年   5篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
22.
Autophagy is an intracellular degradation process for recycling macromolecules and organelles. It plays important roles in plant development and in response to nutritional demand, stress, and senescence. Organisms from yeast to plants contain many autophagy-associated genes (ATG). In this study, we found that a total of 33 ATG homologues exist in the rice [Oryza sativa L. (Os)] genome, which were classified into 13 ATG subfamilies. Six of them are alternatively spliced genes. Evolutional analysis showed that expansion of 10 OsATG homologues occurred via segmental duplication events and that the occurrence of these OsATG homologues within each subfamily was asynchronous. The Ka/Ks ratios suggested purifying selection for four duplicated OsATG homologues and positive selection for two. Calculating the dates of the duplication events indicated that all duplication events might have occurred after the origin of the grasses, from 21.43 to 66.77 million years ago. Semi-quantitative RT–PCR analysis and mining the digital expression database of rice showed that all 33 OsATG homologues could be detected in at least one cell type of the various tissues under normal or stress growth conditions, but their expression was tightly regulated. The 10 duplicated genes showed expression divergence. The expression of most OsATG homologues was regulated by at least one treatment, including hormones, abiotic and biotic stresses, and nutrient limitation. The identification of OsATG homologues showing constitutive expression or responses to environmental stimuli provides new insights for in-depth characterization of selected genes of importance in rice.  相似文献   
23.
Achieving high-performance in all-small-molecule organic solar cells (ASM-OSCs) significantly relies on precise nanoscale phase separation through domain size manipulation in the active layer. Nonetheless, for ASM-OSC systems, forging a clear connection between the tuning of domain size and the intricacies of phase separation proves to be a formidable challenge. This study investigates the intricate interplay between domain size adjustment and the creation of optimal phase separation morphology, crucial for ASM-OSCs’ performance. It is demonstrated that exceptional phase separation in ASM-OSCs’ active layer is achieved by meticulously controlling the continuity and uniformity of domains via re-packing process. A series of halogen-substituted solvents (Fluorobenzene, Chlorobenzene, Bromobenzene, and Iodobenzene) is adopted to tune the re-packing kinetics, the ASM-OSCs treated with CB exhibited an impressive 16.2% power conversion efficiency (PCE). The PCE enhancement can be attributed to the gradual crystallization process, promoting a smoothly interconnected and uniformly distributed domain size. This, in turn, leads to a favorable phase separation morphology, enhanced charge transfer, extended carrier lifetime, and consequently, reduced recombination of free charges. The findings emphasize the pivotal role of re-packing kinetics in achieving optimal phase separation in ASM-OSCs, offering valuable insights for designing high-performance ASM-OSCs fabrication strategies.  相似文献   
24.
25.
26.
Carbonaceous materials have emerged as promising anode candidates for potassium‐ion batteries (PIBs) due to overwhelming advantages including cost‐effectiveness and wide availability of materials. However, further development in this realm is handicapped by the deficiency in their in‐target and large‐scale synthesis, as well as their low specific capacity and huge volume expansion. Herein the precise and scalable synthesis of N/S dual‐doped graphitic hollow architectures (NSG) via direct plasma enhanced chemical vapor deposition is reported. Thus‐fabricated NSG affording uniform nitrogen/sulfur co‐doping, possesses ample potassiophilic surface moieties, effective electron/ion‐transport pathways, and high structural stability, which bestow it with high rate capability (≈100 mAh g?1 at 20 A g?1) and a prolonged cycle life (a capacity retention rate of 90.2% at 5 A g?1 after 5000 cycles), important steps toward high‐performance K‐ion storage. The enhanced kinetics of the NSG anode are systematically probed by theoretical simulations combined with operando Raman spectroscopy, ex situ X‐ray photoelectron spectroscopy, and galvanostatic intermittent titration technique measurements. In further contexts, printed NSG electrodes with tunable mass loading (1.84, 3.64, and 5.65 mg cm?2) are realized to showcase high areal capacities. This study demonstrates the construction of a printable carbon‐based PIB anode, that holds great promise for next‐generation grid‐scale PIB applications.  相似文献   
27.
BMP signaling in vascular diseases   总被引:1,自引:0,他引:1  
  相似文献   
28.
The lesion of nucleus robustus archistriatalis (RA) has no effect on normal short calls in the bramble finch, but affects significantly the temporal and acoustic features of learned long calls. It causes the principal frequency of basic sound in monotone long calls to increase 500 cents, and to lose two upper partials. The lesion of RA not only results in the increased sound length of loud-sound and shortened coda of variable-tone long calls by 13.4%–22.1% and 21.2%–24.2% on average, respectively, but also makes the frequency rising coefficient (FRC) of even order partial tone in loud-sound drop 18.5%–25.8% on an average, and the step-up rate decrease 22.7% –24.0% on an average with the increase of frequencies. These results show that the control of temporal and frequency features of learned calls by RA matches to each other. Moreover, the lesion of bilateral RA can confuse the vocal pattern, and the produced long call has the character of both the mono- and variable-tone long calls. The prelude shows rising frequency, and the loud sound is monotone sound.  相似文献   
29.
30.
Zhang X  Zhang SL  Xiong HY  DU YH  Quan L  Yang J  Ma XR  Liu HR 《生理学报》2011,63(2):149-154
血管紧张素AT1受体抗体(AT1-Ab)可损伤胎盘发育,进而导致胎儿宫内生长受限(intrauterine growth restriction,IUGR).根据胎儿源性成人疾病学说,IUGR会明显增加成人后患心血管疾病的几率.本研究旨在观察AT1-Ab阳性孕鼠后代生长至成年后血管功能有无异常.24只雌性Wistar大...  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号