全文获取类型
收费全文 | 51625篇 |
免费 | 5428篇 |
国内免费 | 23篇 |
出版年
2022年 | 249篇 |
2021年 | 662篇 |
2020年 | 404篇 |
2019年 | 533篇 |
2018年 | 639篇 |
2017年 | 610篇 |
2016年 | 1057篇 |
2015年 | 1951篇 |
2014年 | 1924篇 |
2013年 | 2536篇 |
2012年 | 3016篇 |
2011年 | 2716篇 |
2010年 | 1903篇 |
2009年 | 1695篇 |
2008年 | 2374篇 |
2007年 | 2413篇 |
2006年 | 2171篇 |
2005年 | 2195篇 |
2004年 | 2098篇 |
2003年 | 1866篇 |
2002年 | 1832篇 |
2001年 | 1367篇 |
2000年 | 1342篇 |
1999年 | 1273篇 |
1998年 | 796篇 |
1997年 | 680篇 |
1996年 | 700篇 |
1995年 | 667篇 |
1994年 | 621篇 |
1993年 | 624篇 |
1992年 | 1158篇 |
1991年 | 889篇 |
1990年 | 909篇 |
1989年 | 880篇 |
1988年 | 783篇 |
1987年 | 721篇 |
1986年 | 724篇 |
1985年 | 840篇 |
1984年 | 681篇 |
1983年 | 546篇 |
1982年 | 487篇 |
1981年 | 470篇 |
1980年 | 383篇 |
1979年 | 479篇 |
1978年 | 450篇 |
1977年 | 337篇 |
1976年 | 314篇 |
1975年 | 295篇 |
1974年 | 391篇 |
1973年 | 363篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Eddy van der Maarel 《植被学杂志》2015,26(5):821-825
92.
93.
94.
95.
W. O. van der Knaap Jacqueline F. N. van Leeuwen Tomasz Goslar Robert Krisai Willy Tinner 《Vegetation History and Archaeobotany》2012,21(1):37-60
Three mires and a small lake in the Swiss and Austrian Alps were studied palynologically at high resolution, covering the
last 1,000, 400, 50 and 1,200 years, respectively. Methodological lessons include: (1) Sub-decadal resolution in upper, little-decomposed
peat layers reveals recurrent marked fluctuations in both percentages and influx of regional tree-pollen types, reflecting
variations in pollen production rather than in plant-population sizes. (2) Intermittent, single-spectrum pollen maxima in
samples of sub-decadal resolution indicate pollen transport in clumps. This type of pollen transport may remain unrecognized
in sections with lower sampling resolution, which may then lead to inappropriate interpretation in terms of plant-population
sizes. (3) The detection of short-lived phases of human impact in decomposed peat requires sampling intervals as close as
0.2 cm. (4) PAR (pollen influx) may reflect vegetation dynamics more faithfully than percentages. Reliable PAR, however, is
difficult to achieve in Alpine mires due to past human impact on peat growth, even when complex depth–age modelling techniques
are used. Critical comparison of PAR with percentages is therefore essential. (5) Careful consideration of spatial scales
in pollen signals (local–regional and subdivisions) is essential for a realistic palaeo-ecological interpretation. Results
in terms of past human impact on vegetation are summarized as follows: (1) Trends in pollen types reflecting regional human
action are in general agreement with earlier findings for the western Swiss Alps, allowing for regional differences. (2) All
mires in the Alps investigated here and in an earlier study experienced human impact during the last millennium. The studied
small lake, lying in sub-alpine pasture, records forest dynamics at a lower elevation since a.d. 800. 相似文献
96.
An Ecteola-cellulose chromatography assay for 3′-phosphoadenosine 5′-phosphosulfate: Phenol sulfotransferase 总被引:1,自引:0,他引:1
Ronald T. Borchardt Anna Baranczyk-Kuzma Carol L. Pinnick 《Analytical biochemistry》1983,130(2):334-338
A new assay procedure for phenol sulfotransferase which employs [35S]-3'-phosphoadenosine-5'-phosphosulfate as a sulfate donor and a variety of phenols as sulfate acceptors was developed. The appearance of the 35S-sulfated products or the disappearance of the [35S]-3'-phosphoadenosine-5'-phosphosulfate are determined simultaneously by chromatography of the assay incubation mixtures on Ecteola-cellulose columns, eluting with an NH4HCO3 step gradient. Various acidic, neutral, and basic phenols can be employed as substrates for phenol sulfotransferase using this procedure. 相似文献
97.
Abstract cDNA-RNA liquid hybridization analysis was used to compare the RNA sequence homology between two members of the Nudaurelia β virus family, Trichoplusia ni virus ( T.ni V) and Dasychira pudibunda virus ( D.p V). Heterologous hybridization experiments demonstrated that these viruses shared little sequence homology. Using oligo(dT) chromatography and oligo(dT)12–18 as a primer for cDNA synthesis it was shown that neither T.ni V nor D.p V RNA genomes possess a poly(A) tract at the 3' end. 相似文献
98.
The inner-dune zone between the villages of Bakkum and Egmond in the North-Holland Dune Reserve is one of the few remaining examples of the semi-natural boundary between the dunes and the polders. For several centuries this area has been used for various purposes, in particular for grazing. Large-scale excavating, especially after about 1900, has encroached upon the dunes. Vegetation and land-use history were studied and a provisional scheme on the vegetation development is presented. Management policies discussed are non-intervention, mowing in order to start natural processes such as rabbit grazing, and the continuation of traditional livestock grazing. Proposals for external management policies were made in order to maintain or enhance the original transition zone, based on comprehensive physical-geographical studies of the whole inner-dune zone. 相似文献
99.
Albinism and mouse behaviour 总被引:1,自引:0,他引:1
100.
Abstract Klebsiella pneumoniae M5a1 grows readily on two compounds, 4-hydroxyphenylacetate and 4-aminobutyrate, whose catabolism produces succinic semialdehyde. A single succinic semialdehyde dehydrogenase was detected, native molecular weight 52000, that has NAD as the preferred cofactor and is induced by succinic semialdehyde functions in the oxidation of succinic semialdehyde during growth on both 4-hydroxyphenyl-acetate and 4-aminobutyrate. This contrasts with the situation for Escherichia coli and Pseudomonas putida where two distinct forms of succinic semialdehyde dehydrogenase have been observed. 相似文献