全文获取类型
收费全文 | 36286篇 |
免费 | 2690篇 |
国内免费 | 6篇 |
专业分类
38982篇 |
出版年
2023年 | 211篇 |
2022年 | 357篇 |
2021年 | 639篇 |
2020年 | 479篇 |
2019年 | 537篇 |
2018年 | 1288篇 |
2017年 | 1100篇 |
2016年 | 1271篇 |
2015年 | 1735篇 |
2014年 | 1776篇 |
2013年 | 2312篇 |
2012年 | 2783篇 |
2011年 | 2475篇 |
2010年 | 1683篇 |
2009年 | 1441篇 |
2008年 | 1933篇 |
2007年 | 1864篇 |
2006年 | 1804篇 |
2005年 | 1600篇 |
2004年 | 1547篇 |
2003年 | 1352篇 |
2002年 | 1301篇 |
2001年 | 676篇 |
2000年 | 594篇 |
1999年 | 544篇 |
1998年 | 367篇 |
1997年 | 263篇 |
1996年 | 271篇 |
1995年 | 272篇 |
1994年 | 200篇 |
1993年 | 198篇 |
1992年 | 319篇 |
1991年 | 316篇 |
1990年 | 246篇 |
1989年 | 247篇 |
1988年 | 220篇 |
1987年 | 184篇 |
1986年 | 188篇 |
1985年 | 209篇 |
1984年 | 166篇 |
1983年 | 132篇 |
1982年 | 112篇 |
1981年 | 117篇 |
1980年 | 111篇 |
1979年 | 133篇 |
1978年 | 117篇 |
1976年 | 113篇 |
1975年 | 104篇 |
1974年 | 100篇 |
1973年 | 107篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
E Estébanez-Perpi?á A Bayés J Vendrell M A Jongsma D P Bown J A Gatehouse R Huber W Bode F X Avilés D Reverter 《Journal of molecular biology》2001,313(3):629-638
The cotton bollworm Helicoverpa armigera (Hubner) (Lepidoptera: Noctuidae) is one of the most serious insect pests in Australia, India and China. The larva causes substantial economical losses to legume, fibre, cereal oilseed and vegetable crops. This pest has proven to be difficult to control by conventional means, mainly due to the development of pesticide resistance. We present here the 2.5 A crystal structure from the novel procarboxypeptidase (PCPAHa) found in the gut extracts from H. armigera larvae, the first one reported for an insect. This metalloprotease is synthesized as a zymogen of 46.6 kDa which, upon in vitro activation with Lys-C endoproteinase, yields a pro-segment of 91 residues and an active carboxypeptidase moiety of 318 residues. Both regions show a three-dimensional structure quite similar to the corresponding structures in mammalian digestive carboxypeptidases, the most relevant structural differences being located in the loops between conserved secondary structure elements, including the primary activation site. This activation site contains the motif (Ala)(5)Lys at the C terminus of the helix connecting the pro- and the carboxypeptidase domains. A remarkable feature of PCPAHa is the occurrence of the same (Ala)(6)Lys near the C terminus of the active enzyme. The presence of Ser255 in PCPAHa instead of Ile and Asp found in the pancreatic A and B forms, respectively, enlarges the S1' specificity pocket and influences the substrate preferences of the enzyme. The C-terminal tail of the leech carboxypeptidase inhibitor has been modelled into the PCPAHa active site to explore the substrate preferences and the enzymatic mechanism of this enzyme. 相似文献
2.
François Frappier Andrée Marquet 《Biochemical and biophysical research communications》1981,103(4):1288-1293
[3-14C, 35S]-L-cysteine was tested as precursor of biotin in Achromobacter IVSW. No significant incorporation was observed, in contradiction with the data previously reported. On the other hand, Achromobacter IVSW converts [3H, 14C]-dethiobiotin into biotin. This suggests that biotin is biosynthesized in Achromobacter according to the classical dethiobiotin pathway. 相似文献
3.
Sebastián Moran Miguel Vizoso Anna Martinez-Cardús Antonio Gomez Xavier Matías-Guiu Sebastián M Chiavenna Andrés G Fernandez Manel Esteller 《Epigenetics》2014,9(6):829-833
A formalin-fixed paraffin-embedded (FFPE) sample usually yields highly degraded DNA, which limits the use of techniques requiring high-quality DNA, such as Infinium Methylation microarrays. To overcome this restriction, we have applied an FFPE restoration procedure consisting of DNA repair and ligation processes in a set of paired fresh-frozen (FF) and FFPE samples. We validated the FFPE results in comparison with matched FF samples, enabling us to use FFPE samples on the Infinium HumanMethylation450 Methylation array. 相似文献
4.
5.
6.
7.
E. Molina Grima J. A. Sánchez Pérez F. García Camacho F. G. Acién Fernández J. M. Fernández Sevilla F. Valdés Sanz 《Biotechnology letters》1994,16(10):1035-1040
Summary Eicosapentaenoic acid (EPA) volumetric productivity from an outdoor chemostat culture ofPhaeodactylum tricornutum UTEX 640 in a 50-l tubular photobioreactor varies with dilution rate, reaching a maximum of 47.8 mg l–1 d–1 at D=0.36 d–1. Continuous culture at high dilution rates' is proposed as the most adequate operating mode to maximize polyunsaturated fatty acid production. 相似文献
8.
9.
10.
Xiao-Guo Xiang Wei-Tao Jin De-Zhu Li André Schuiteman Wei-Chang Huang Jian-Wu Li Xiao-Hua Jin Zhen-Yu Li 《PloS one》2014,9(1)
Collabieae (Orchidaceae) is a long neglected tribe with confusing tribal and generic delimitation and little-understood phylogenetic relationships. Using plastid matK, psaB, rbcL, and trnH-psbA DNA sequences and morphological evidence, the phylogenetic relationships within the tribe Collabieae were assessed as a basis for revising their tribal and generic delimitation. Collabieae (including the previously misplaced mycoheterotrophic Risleya) is supported as monophyletic and nested within a superclade that also includes Epidendreae, Podochileae, Cymbidieae and Vandeae. Risleya is nested in Collabiinae and sister to Chrysoglossum, a relationship which, despite their great vegetative differences, is supported by floral characters. Ania is a distinct genus supported by both morphological and molecular evidence, while redefined Tainia includes Nephelaphyllum and Mischobulbum. Calanthe is paraphyletic and consists four clades; the genera Gastrorchis, Phaius and Cephalantheropsis should be subsumed within Calanthe. Calanthe sect. Ghiesbreghtia is nested within sect. Calanthe, to which the disputed Calanthe delavayi belongs as well. Our results indicate that, in Collabieae, habit evolved from being epiphytic to terrestrial. 相似文献