全文获取类型
收费全文 | 4442篇 |
免费 | 219篇 |
国内免费 | 26篇 |
出版年
2023年 | 82篇 |
2022年 | 108篇 |
2021年 | 342篇 |
2020年 | 176篇 |
2019年 | 203篇 |
2018年 | 274篇 |
2017年 | 175篇 |
2016年 | 259篇 |
2015年 | 308篇 |
2014年 | 336篇 |
2013年 | 371篇 |
2012年 | 363篇 |
2011年 | 306篇 |
2010年 | 188篇 |
2009年 | 172篇 |
2008年 | 184篇 |
2007年 | 166篇 |
2006年 | 120篇 |
2005年 | 125篇 |
2004年 | 86篇 |
2003年 | 70篇 |
2002年 | 56篇 |
2001年 | 13篇 |
2000年 | 14篇 |
1999年 | 19篇 |
1998年 | 10篇 |
1997年 | 11篇 |
1996年 | 8篇 |
1995年 | 11篇 |
1994年 | 9篇 |
1993年 | 15篇 |
1992年 | 10篇 |
1991年 | 10篇 |
1990年 | 8篇 |
1989年 | 11篇 |
1988年 | 6篇 |
1987年 | 11篇 |
1986年 | 4篇 |
1985年 | 4篇 |
1984年 | 6篇 |
1983年 | 2篇 |
1982年 | 9篇 |
1981年 | 4篇 |
1980年 | 4篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1977年 | 3篇 |
1974年 | 4篇 |
1973年 | 2篇 |
1972年 | 2篇 |
排序方式: 共有4687条查询结果,搜索用时 15 毫秒
1.
Raza Shahbaz Mohsin Mashkoor Madni Waqas Ahmed Sarwar Fatima Saqib Muhammad Aslam Bilal 《EcoHealth》2017,14(1):182-186
EcoHealth - We investigated wild migratory birds faecal swabs for extended-spectrum β-lactamases-producing Klebsiella pneumoniae (ESBL-K. pneumoniae) from wetland habitats in Pakistan. ESBL-K.... 相似文献
2.
3.
Ronac Mamtani James D. Lewis Frank I. Scott Tariq Ahmad David S. Goldberg Jashodeep Datta Yu-Xiao Yang Ben Boursi 《PLoS medicine》2016,13(4)
BackgroundSeveral prior studies have found an association between statin use and reduced risk of colorectal cancer. We hypothesized that these findings may be due to systematic bias and examined the independent association of colorectal cancer risk with statin use, serum cholesterol, and change in cholesterol concentration.ConclusionsAlthough the risk of colorectal cancer was lower in statin users versus nonusers, no difference was observed among those who continued versus discontinued statin therapy, suggesting the potential for indication bias. The association between decreased serum cholesterol and colorectal cancer risk suggests a cholesterol-lowering effect of undiagnosed malignancy. Clinical judgment should be used when considering causes of cholesterol reduction in patients, including those on statin therapy. 相似文献
4.
5.
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
6.
Summary Ligninolytic enzyme activities in cell-free culture filtrates of Coriolus versicolor, Fusarium solani and Phanaerochaete chrysosporium were assessed using a veratryl alcohol oxidation assay system and results compared with those obtained using a relatively new assay system based on the oxidation of Azure B. 相似文献
7.
8.
Muhammad Yaseen Muhammad Zahir Aziz Abdul Aleem Jafar Muhammad Naveed 《International journal of phytoremediation》2016,18(5):502-508
A field experiment in collaboration with a private textile industry (Noor Fatima Fabrics Private (Ltd.), Faisalabad) was conducted to evaluate the effect of disposed water from bleaching unit, printing unit and end drain for improving growth and yield of wheat under saline sodic soil. Textile waste water along with canal water (control) was applied with and without liquid NPK fertilizer. The application of liquid NPK fertilizer with end drain waste water increased plant height, spike length, flag leaf length, root length, number of tillers (m?2), number of fertile tillers (m?2), 1000 grain weight, grain yield, straw yield and biological yield up to 21, 20, 20, 44, 17, 20, 14, 44, 40 and 41%, respectively compared to canal water (control). Similarly, the NPK uptake in grain was increased up to 15, 30 and 28%, respectively by liquid fertilizer treated end drain water as compare to canal water with liquid fertilizer. Moreover, concentration of different heavy metals particularly Cu, Cr, Pb and Cd was decreased in grains by application of waste water along with liquid NPK. The result may imply that waste water application along with liquid-NPK could be a novel approach for improving growth and yield of wheat in saline sodic soils. 相似文献
9.
Mushtaq Hussain Syeda Qamarunnissa Saboohi Raza Javed Qureshi Abdul Wajid Sheikh A. Rasool 《Biologia》2009,64(5):852-858
DNA photolyase is perhaps the most ancient and direct arsenal in curing the UV-induced dimers formed in the microbial genome.
Out of two cofactors of the enzyme, catalytic and light harvesting, differences in the latter have provided basis for categorizing
photolyases of prokaryotes as folate and deazaflavin types. In the present study, the homology modeling of DNA photolyase
of Enterococcus faecalis was undertaken. The predicted models were structurally compared with the crystal structure coordinates of photolyases from
Escherichia coli (folate type) and Anacystis nidulans (deazaflavin type). Discrepancies present in the multiple sequence alignment and tertiary structures, particularly at the
light harvesting cofactor (methenyltetrahydrofolic acid, MTHF; 8-hydroxy-5-deazaflavin, 8-HDF) binding sites indicated the
mechanistic nature of enterococcal photolyase. Concisely, despite the greater holistic homology with folate-type photolyase,
enterococcal photolyase was characterized as deazaflavin-type. The presence of 8-HDF binding sites and groove architecture
of substrate binding sites were also found supportive in this regard. The inter cofactor distance and/or orientation also
implied to the efficient energy transfer in photolyase of Enterococcus in comparison with E. coli. In addition, we observed relatively high protein deformability in the enterococcal genome, which may favors the repair action
of photolyase. The findings are expected to provide molecular insights into the difference in sunlight inactivation rate of
two important fecal contamination indicators, namely Enterococcus and E. coli. 相似文献
10.
Perspective texture synthesis has great significance in many fields like video editing, scene capturing etc., due to its ability to read and control global feature information. In this paper, we present a novel example-based, specifically energy optimization-based algorithm, to synthesize perspective textures. Energy optimization technique is a pixel-based approach, so it’s time-consuming. We improve it from two aspects with the purpose of achieving faster synthesis and high quality. Firstly, we change this pixel-based technique by replacing the pixel computation with a little patch. Secondly, we present a novel technique to accelerate searching nearest neighborhoods in energy optimization. Using k- means clustering technique to build a search tree to accelerate the search. Hence, we make use of principal component analysis (PCA) technique to reduce dimensions of input vectors. The high quality results prove that our approach is feasible. Besides, our proposed algorithm needs shorter time relative to other similar methods. 相似文献