全文获取类型
收费全文 | 48263篇 |
免费 | 3669篇 |
国内免费 | 3533篇 |
专业分类
55465篇 |
出版年
2024年 | 120篇 |
2023年 | 580篇 |
2022年 | 1375篇 |
2021年 | 2228篇 |
2020年 | 1520篇 |
2019年 | 1927篇 |
2018年 | 2053篇 |
2017年 | 1679篇 |
2016年 | 2173篇 |
2015年 | 2510篇 |
2014年 | 3224篇 |
2013年 | 3489篇 |
2012年 | 3981篇 |
2011年 | 3721篇 |
2010年 | 2633篇 |
2009年 | 2303篇 |
2008年 | 2643篇 |
2007年 | 2375篇 |
2006年 | 2080篇 |
2005年 | 1712篇 |
2004年 | 1602篇 |
2003年 | 1504篇 |
2002年 | 1225篇 |
2001年 | 1000篇 |
2000年 | 840篇 |
1999年 | 615篇 |
1998年 | 382篇 |
1997年 | 318篇 |
1996年 | 307篇 |
1995年 | 318篇 |
1994年 | 291篇 |
1993年 | 225篇 |
1992年 | 290篇 |
1991年 | 259篇 |
1990年 | 208篇 |
1989年 | 192篇 |
1988年 | 129篇 |
1987年 | 175篇 |
1986年 | 145篇 |
1985年 | 130篇 |
1984年 | 101篇 |
1983年 | 95篇 |
1982年 | 82篇 |
1981年 | 78篇 |
1980年 | 52篇 |
1979年 | 62篇 |
1978年 | 66篇 |
1976年 | 51篇 |
1973年 | 63篇 |
1972年 | 52篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
181.
Two forms of type-1 protein phosphatase activating factor (FA) termed FA1 and FA2 have been identified in plasma membranes of pig brain. FA1 is spontaneously active and trypsin-labile whereas FA2 is inactive and trypsin-resistant. Phospholipid reconstitution studies further indicate that the FA activity in the neutral phospholipids-reconstituted complex is spontaneously active and trypsin-labile whereas the FA activity in the acidic phospholipids-reconstituted complex is trypsin-resistant and inactive. The results indicate that inactive FA2 may have its catalytic domain interacted with negatively-charged phospholipids in brain membranes. This provides initial evidence for the regulation of protein kinase FA (a transmembrane signal of insulin and epidermal growth factor) in the central nervous system. 相似文献
182.
183.
Dear Editor,
Sex determination is one of the most fundamental develop-ment processes,as gender is the first and most important identity of human.In most mammals... 相似文献
184.
Chen Lu Zhongti Sun Lianghao Yu Xueyu Lian Yuyang Yi Jie Li Zhongfan Liu Shixue Dou Jingyu Sun 《Liver Transplantation》2020,10(28)
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
185.
186.
187.
Plant defense responses need to be tightly regulated to prevent auto-immunity, which is detrimental to growth and development. To identify negative regulators of Resistance (R) protein-mediated resistance, we screened for mutants with constitutive defense responses in the npr1-1 background. Map-based cloning revealed that one of the mutant genes encodes a conserved TPR domain-containing protein previously known as SRFR1 (SUPPRESSOR OF rps4-RLD). The constitutive defense responses in the srfr1 mutants in Col-0 background are suppressed by mutations in SNC1, which encodes a TIR-NB-LRR (Toll Interleukin1 Receptor-Nucleotide Binding-Leu-Rich Repeat) R protein. Yeast two-hybrid screens identified SGT1a and SGT1b as interacting proteins of SRFR1. The interactions between SGT1 and SRFR1 were further confirmed by co-immunoprecipitation analysis. In srfr1 mutants, levels of multiple NB-LRR R proteins including SNC1, RPS2 and RPS4 are increased. Increased accumulation of SNC1 is also observed in the sgt1b mutant. Our data suggest that SRFR1 functions together with SGT1 to negatively regulate R protein accumulation, which is required for preventing auto-activation of plant immunity. 相似文献
188.
Rytis Prekeris Judith Klumperman Yu A. Chen Richard H. Scheller 《The Journal of cell biology》1998,143(4):957-971
Endocytosis-mediated recycling of plasma membrane is a critical vesicle trafficking step important in diverse biological processes. The membrane trafficking decisions and sorting events take place in a series of heterogeneous and highly dynamic organelles, the endosomes. Syntaxin 13, a recently discovered member of the syntaxin family, has been suggested to play a role in mediating endosomal trafficking. To better understand the function of syntaxin 13 we examined its intracellular distribution in nonpolarized cells. By confocal immunofluorescence and electron microscopy, syntaxin 13 is primarily found in tubular early and recycling endosomes, where it colocalizes with transferrin receptor. Additional labeling is also present in endosomal vacuoles, where it is often found in clathrin-coated membrane areas. Furthermore, anti-syntaxin 13 antibody inhibits transferrin receptor recycling in permeabilized PC12 cells. Immunoprecipitation of syntaxin 13 revealed that, in Triton X-100 extracts, syntaxin 13 is present in a complex(es) comprised of βSNAP, VAMP 2/3, and SNAP-25. This complex(es) binds exogenously added αSNAP and NSF and dissociates in the presence of ATP, but not ATPγS. These results support a role for syntaxin 13 in membrane fusion events during the recycling of plasma membrane proteins. 相似文献
189.
空间异质性对样地数据空间外推的影响 总被引:1,自引:0,他引:1
应用模型结合的方法模拟了3个空间异质性等级预案下反应变量(气候变化下景观水平的树种分布面积)的变化情况,并分析模拟结果在预案之间的差异性,探讨了环境空间异质性对样地观测到的树种对气候变化响应向更大空间尺度外推的影响.结果表明:空间异质性在一般情况下对样地数据向土地类型尺度外推没有影响,而对样地尺度外推到海拔带尺度的影响则有较复杂的情况.对于对气候变化不敏感的树种以及非地带性树种,空间异质性对样地数据向海拔带尺度外推没有影响;对于大多数对气候变化敏感的地带性树种而言,空间异质性对样地数据向海拔带尺度外推则有影响. 相似文献
190.