全文获取类型
收费全文 | 23600篇 |
免费 | 1841篇 |
国内免费 | 16篇 |
专业分类
25457篇 |
出版年
2023年 | 108篇 |
2022年 | 241篇 |
2021年 | 463篇 |
2020年 | 275篇 |
2019年 | 389篇 |
2018年 | 468篇 |
2017年 | 413篇 |
2016年 | 657篇 |
2015年 | 1115篇 |
2014年 | 1272篇 |
2013年 | 1540篇 |
2012年 | 1803篇 |
2011年 | 1661篇 |
2010年 | 1084篇 |
2009年 | 1009篇 |
2008年 | 1291篇 |
2007年 | 1207篇 |
2006年 | 1202篇 |
2005年 | 1162篇 |
2004年 | 1105篇 |
2003年 | 970篇 |
2002年 | 1024篇 |
2001年 | 295篇 |
2000年 | 230篇 |
1999年 | 278篇 |
1998年 | 289篇 |
1997年 | 216篇 |
1996年 | 240篇 |
1995年 | 216篇 |
1994年 | 227篇 |
1993年 | 228篇 |
1992年 | 202篇 |
1991年 | 162篇 |
1990年 | 135篇 |
1989年 | 145篇 |
1988年 | 157篇 |
1987年 | 108篇 |
1986年 | 103篇 |
1985年 | 122篇 |
1984年 | 148篇 |
1983年 | 117篇 |
1982年 | 143篇 |
1981年 | 118篇 |
1980年 | 112篇 |
1979年 | 95篇 |
1978年 | 93篇 |
1977年 | 86篇 |
1976年 | 62篇 |
1974年 | 59篇 |
1973年 | 66篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Jan Ahlers 《Molecular and cellular biochemistry》1977,15(2):145-148
Summary Bound and solubilized ATPase from Escherichia coli show similar kinetic properties. The saturation curves for MgATP are hyperbolic with both preparations. The straight lines in the Line-weaver–Burk plot indicate that MgATP is the true substrate, that one molecule MgATP is bound per enzyme molecule, and that there is no cooperativity. Presence of EDTA leads to sigmoidal saturation curves. This effect could be reversed by adding MgCl2 stoichiometrically to EDTA.Different results in other publications, especially in that ofCarreira andMuñoz can be explained as being primarily the consequence of complexing agent contaminations in the assay. 相似文献
62.
Jan Jeník 《Folia Geobotanica》1977,12(2):208-208
63.
64.
Historical phytoplankton data of the Marsdiep 总被引:4,自引:0,他引:4
Published and unpublished data on phytoplankton of the Marsdiep tidal inlet were studied. Most older data, going back to 1897, are based on net-phytoplankton only, the earliest quantitative (Utermöhl) data being from 1965.Phaeocystis sp. bloomed in the Marsdiep after a spring diatom peak, at least as long ago as 1897. Summer or automn peaks ofPhaeocystis sp., frequent now, were also observed in 1898 and 1899. The duration of thePhaeocystis blooms in 1897 to 1899 was shorter than observed after 1978, but longer than in the early 1970s. The recent (1987 to 1989) duration ofPhaeocystis blooms is 2 to 3 times that of 1897–1899. This increase surpasses normal yearly variation and can be related to anthropogenically caused in crease in nutrient concentrations. A number of diatomspecies, at present numerically dominant in the spring peak, are not mentioned as dominant in the earlier periods of observation. They are small and passed through the nets used.Biddulphia sinensis, at present often abundant, is an immigrant in the North Sea since 1903, and for that reason absent from the earliest Marsdiep observations. No clear trend in duration of diatom blooms is apparent during 1965 to 1989. Anthropogenic eutrophication did not affect diatom blooms. Marsdiep records in the literature ofPhaeocystis globosa, P. pouchetii andP. sp. all refer to the same species. 相似文献
65.
Crustacea Malacostraca were hitherto unknown from fresh waters of the Canary Islands. A new species of Amphipoda, Rhipidogammarus rheophilus, has recently been discovered in springs and spring brooks in Tenerife.
Resumen Crustacea Malacostraca era hasta ahora desconocida de las aguas dulces de las Islas Canarias. Una nueva especie de anfípodo, Rhipidogammarus rheophilus, ha sido recientemente descubierto de fuentes y manantiales de Tenerife.相似文献
66.
67.
Summary The reasons behind the absence of the prawn Palaemon adspersus and the presence of P. squilla in rockpools and on bare sand bottoms were studied. Some maximal abundances in different habitats are given. Introduction experiments into natural and artificial rockpools and measurements of tolerance towards low oxygen levels showed that nocturnal hypoxia excluded P. adspersus which was significantly more sensitive to oxygen depletion. Respiration rates measured by the closed-bottle method showed no interspecific difference.On bare sand bottoms P. aspersus was probably excluded by predators, since predator exclusion experiments in cages and predator inclusion experiments in containers showed that P. adaspersus was more vulnerable to predation than P. squilla.The costs for being able to cope with a wide array of habitat in P. squilla are probably balanced by the benefits of access to habitats such as intertidal rockpools, very shallow bottoms and deeper sand bottoms. Tolerance towards abiotic factors extends its habitat range upwards into shallower waters, and tolerance towards biotic factors, i.e. predation, extends it downwards. 相似文献
68.
Solid-phase peptide synthesis of somatostatin using mild base cleavage of N alpha-9-fluorenylmethyloxycarbonylamino acids 总被引:3,自引:0,他引:3
C D Chang A M Felix M H Jimenez J Meienhofer 《International journal of peptide and protein research》1980,15(5):485-494
Experimental details for the "Fmoc solid phase peptide synthesis" of somatostatin are described. The 9-fluorenylmethyloxycarbonyl group was rapidly and quantitatively cleaved by 55% piperidine in dimethylformamide and monitored (u.v.) manually. For a kinetic study, a centrifugal reactor with a photometric control system and reference cell was used at each stage. The symmetrical anhydride coupling reaction was rapid and either acetic anhydride or fluorescamine termination was incorporated to minimize formation of deletion peptides. Anchor-bond cleavage was effected with trifluoroacetic acid which simultaneously removed all the acid labile tert.-butyl side chain protecting groups. N alpha-9-fluorenylmethyloxycarbonyl peptides may be obtained by omitting the piperidine deprotection step after the last cycle of synthesis. From several syntheses, analytically pure di-S-protected somatostatin 14-peptide was obtained in 55-60% overall yield. The S-protecting groups were removed and the product was purified by gel filtration to give homogeneous dihydrosomatostatin (91%) yield. Oxidation of dihydrosomatostatin with potassium ferricyanide and purification by countercurrent distribution provided analytically pure homogeneous somatostatin. 相似文献
69.
70.