全文获取类型
收费全文 | 14989篇 |
免费 | 1297篇 |
国内免费 | 876篇 |
专业分类
17162篇 |
出版年
2024年 | 29篇 |
2023年 | 177篇 |
2022年 | 381篇 |
2021年 | 651篇 |
2020年 | 439篇 |
2019年 | 494篇 |
2018年 | 516篇 |
2017年 | 344篇 |
2016年 | 539篇 |
2015年 | 920篇 |
2014年 | 995篇 |
2013年 | 1119篇 |
2012年 | 1338篇 |
2011年 | 1174篇 |
2010年 | 733篇 |
2009年 | 608篇 |
2008年 | 781篇 |
2007年 | 717篇 |
2006年 | 646篇 |
2005年 | 537篇 |
2004年 | 473篇 |
2003年 | 426篇 |
2002年 | 356篇 |
2001年 | 323篇 |
2000年 | 290篇 |
1999年 | 273篇 |
1998年 | 141篇 |
1997年 | 124篇 |
1996年 | 117篇 |
1995年 | 106篇 |
1994年 | 125篇 |
1993年 | 83篇 |
1992年 | 129篇 |
1991年 | 138篇 |
1990年 | 103篇 |
1989年 | 111篇 |
1988年 | 93篇 |
1987年 | 86篇 |
1986年 | 72篇 |
1985年 | 46篇 |
1984年 | 49篇 |
1983年 | 34篇 |
1982年 | 24篇 |
1981年 | 24篇 |
1979年 | 29篇 |
1978年 | 28篇 |
1976年 | 25篇 |
1975年 | 22篇 |
1974年 | 27篇 |
1973年 | 27篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
3.
Structural Insight of a Trimodular Halophilic Cellulase with a Family 46 Carbohydrate-Binding Module
Huaidong Zhang Guimin Zhang Chaoxiang Yao Muhammad Junaid Zhenghui Lu Houjin Zhang Yanhe Ma 《PloS one》2015,10(11)
Cellulases are the key enzymes used in the biofuel industry. A typical cellulase contains a catalytic domain connected to a carbohydrate-binding module (CBM) through a flexible linker. Here we report the structure of an atypical trimodular cellulase which harbors a catalytic domain, a CBM46 domain and a rigid CBM_X domain between them. The catalytic domain shows the features of GH5 family, while the CBM46 domain has a sandwich-like structure. The catalytic domain and the CBM46 domain form an extended substrate binding cleft, within which several tryptophan residues are well exposed. Mutagenesis assays indicate that these residues are essential for the enzymatic activities. Gel affinity electrophoresis shows that these tryptophan residues are involved in the polysaccharide substrate binding. Also, electrostatic potential analysis indicates that almost the entire solvent accessible surface of CelB is negatively charged, which is consistent with the halophilic nature of this enzyme. 相似文献
4.
Jian Xiao Dan Chen Xiu-Xian Lin Shi-Fang Peng Mei-Fang Xiao Wei-Hua Huang Yi-Cheng Wang Jing-Bo Peng Wei Zhang Dong-Sheng Ouyang Yao Chen 《PloS one》2016,11(2)
Ginsenoside compound K (CK), a rare ginsenoside originating from Panax Ginseng, has been found to possess unique pharmacological activities specifically as anti-cancers. However, the role of cytochrome P450s (CYPs) in the metabolism of CK is unclear. In this study, we screened the CYPs for the metabolism of CK in vitro using human liver microsomes (HLMs) or human recombinant CYPs. The results showed that CK inhibited the enzyme activities of CYP2C9 and CYP3A4 in the HLMs. The Km and Vmax values of CK were 84.20±21.92 μM and 0.28±0.04 nmol/mg protein/min, respectively, for the HLMs; 34.63±10.48 μM and 0.45±0.05 nmol/nmol P450/min, respectively, for CYP2C9; and 27.03±5.04 μM and 0.68±0.04 nmol/nmol P450/min, respectively, for CYP3A4. The IC50 values were 16.00 μM and 9.83 μM, and Ki values were 14.92 μM and 11.42μM for CYP2C9 and CYP3A4, respectively. Other human CYP isoforms, including CYP1A2, CYP2A6, CYP2D6, CYP2E1, and CYP2C19, showed minimal or no effect on CK metabolism. The results suggested that CK was a substrate and also inhibitors for both CYP2C9 and CYP3A4. Patients using CK in combination with therapeutic drugs that are substrates of CYP2C9 and CYP3A4 for different reasons should be careful, although the inhibiting potency of CK is much poorer than that of enzyme-specific inhibitors. 相似文献
5.
6.
7.
8.
S C Tsai R Adamik V C Manganiello M Vaughan 《Biochemical and biophysical research communications》1981,100(2):637-643
A new amino acid was isolated from the cuticle collagen of and characterized by ultraviolet, mass and nmr spectroscopies and chemical degradation. The results indicate that the compound is an isomer of trityrosine, having an ether linkage. The name “isotrityrosine” is proposed. Its structure suggests that it serves as a crosslink and plays a role in the organization of the collagen structure. 相似文献
9.
Y. Saijo S. Takeda A. Scherer T. Kobayashi Y. Mada H. Taniguchi M. Yao S. Wakatsuki 《Protein science : a publication of the Protein Society》1997,6(4):916-918
Troponin is a ternary protein complex consisting of subunits TnC. TnI, and TnT, and plays a key role in calcium regulation of the skeletal and cardiac muscle contraction. In the present study, a partial complex (CI47) was prepared from Escherichia coli-expressed rabbit skeletal muscle TnC and fragment 1-47 of TnI, which is obtained by chemical cleavage of an E. coli-expressed mutant of rabbit skeletal muscle TnI. Within the ternary troponin complex, CI47 is thought to form a core that is resistant to proteolytic digestion, and the interaction within CI47 likely maintains the integrity of the troponin complex. Complex CI47 was crystallized in the presence of sodium citrate. The addition of trehalose improved the diffraction pattern of the crystals substantially. The crystal lattice belongs to the space group P3(1)(2)21, with unit cell dimensions a = b = 48.2 A, c = 162 A. The asymmetric unit presumably contains one CI47 complex. Soaking with p-chloromercuribenzenesulfonate (PCMBS) resulted in loss of isomorphism, but enhanced the quality of the crystals. The crystals diffracted up to 2.3 A resolution, with completeness of 91% and R(merge) = 6.4%. The crystals of PCMBS-derivative should be suitable for X-ray studies using the multiple-wavelength anomalous diffraction technique. This is the first step for elucidating the structure of the full troponin complex. 相似文献
10.
Kun-Nan Tsai Guang-Wu Chen Calvin Yu-Chian Chen 《Journal of biomolecular structure & dynamics》2013,31(5):1089-1099
Abstract The resonances of the protonated carbons of [d(TAGCGCTA)]2 have been assigned by the two-dimensional proton-detected double-quantum heteronuclear correlation experiment ([1H-l3C]-DQCOSY). 13C-coupled and l3C-decoupled versions of the experiment were used. The assignment method is discussed in detail. The deoxyribose cross peaks segregate into five well-resolved regions, and the base cross peaks have distinct features that are helpful for assignments. The cross peaks from the 1H-13C pairs at the Cyd5, Ado2 and ThdCH3 base positions fall in separate regions of the spectrum from each other; they also are resolved from the closely spaced Ado8, Guo8, Cyd6 and Thd6. Additional parameters for distinction of the base signals are their differing J-coupling values and long-range coupling patterns. 相似文献