全文获取类型
收费全文 | 72440篇 |
免费 | 5956篇 |
国内免费 | 37篇 |
专业分类
78433篇 |
出版年
2022年 | 632篇 |
2021年 | 1169篇 |
2020年 | 872篇 |
2019年 | 935篇 |
2018年 | 1483篇 |
2017年 | 1242篇 |
2016年 | 2054篇 |
2015年 | 3067篇 |
2014年 | 2977篇 |
2013年 | 3886篇 |
2012年 | 4631篇 |
2011年 | 4333篇 |
2010年 | 2623篇 |
2009年 | 2426篇 |
2008年 | 3344篇 |
2007年 | 3310篇 |
2006年 | 3068篇 |
2005年 | 3346篇 |
2004年 | 3236篇 |
2003年 | 2783篇 |
2002年 | 2355篇 |
2001年 | 1854篇 |
2000年 | 1801篇 |
1999年 | 1598篇 |
1998年 | 731篇 |
1997年 | 684篇 |
1996年 | 709篇 |
1995年 | 605篇 |
1994年 | 583篇 |
1993年 | 533篇 |
1992年 | 1161篇 |
1991年 | 1046篇 |
1990年 | 963篇 |
1989年 | 918篇 |
1988年 | 926篇 |
1987年 | 834篇 |
1986年 | 780篇 |
1985年 | 746篇 |
1984年 | 701篇 |
1983年 | 537篇 |
1982年 | 424篇 |
1981年 | 440篇 |
1980年 | 392篇 |
1979年 | 553篇 |
1978年 | 473篇 |
1977年 | 383篇 |
1976年 | 347篇 |
1975年 | 380篇 |
1974年 | 394篇 |
1973年 | 372篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
72.
Covalent dimerization of the adrenocorticotropin fragment ACTH11-24 increases its antagonistic potency on the ACTH-induced steroidogenesis in isolated bovine fasciculata/reticularis cells by 3 orders of magnitude when the C-termini are linked via a 10 A long spacer. This strong potentiation, probably mediated by cross-linking of the receptors, was shown to be dependent on the point of attachment of the monomeric fragment to the spacer, thus providing information about the position of the binding site in the hormonal segment and about the distance of the receptors on the cell surface. 相似文献
73.
In the River Lobos-Ucero and its tributary the River Avión-Milanos (Duero basin, Old Castile, Central Spain), two limestone streams fed by aquifers, the population of brown trout, as compared with the populations of other European streams, shows a high growth rate, high condition coefficients, short life-span and early age at first maturity. Gonad cycle was also studied. Size distributions of unshed eggs exhibit a dynamic activity with a bi-modal distribution from June onwards, spawning occurred in the last days of November. Fecundity (F) can be predicted from trout length (L, mm) according to the equation: F= –646.47+5.6167 · L. Numbers and standing crop of trout range from 18 to 3903 ind. ha–1 and 3.6 to 452.9 Kg ha–1, reaching higher values in the sites close to the aquifers. Egg production had values of 22.4 and 18.0 eggs m–2 in the Rivers Ucero and Avión-Milanos respectively. Some factors suggested as regulators of these demographical characteristics are discussed in the light of recent literature. 相似文献
74.
Berta Fiszer-Szafarz David Szafarz Alba Guevara de Murillo 《Analytical biochemistry》1981,110(1):165-170
A fluorometric method using 3,5-diaminobenzoic acid for DNA determination in tissues, cultured cells, nucleated blood cells, and yeast cells is described. The method is general, simple, and rapid, and does not require prior DNA extraction, since tissue is directly solubilized in Triton X-100 and ammonia. The procedure is highly sensitive, and is able to measure rather accurately as little as 10 ng of DNA. It is applicable to all types of DNA structure. The DNA content determined in various tissues and cells was: 2.50 mg/g fresh rat liver, 3.32 mg/g rat diethylnitrosamine-induced hepatoma, 2.49 mg/g fresh mouse liver, 8.76 μg/106 human leukocytes, 3.37 μg/106 chicken fibroblasts, 2.97 μg/108 haploid yeast cells, and 2.84 μg/108 haploid yeast protoplasts. 相似文献
75.
Electrocardiogram (ECG) analysis was performed in three human divers studied at 21 and 23.5 ATA while they breathed various gas mixtures containing H2 and/or He (COMEX HYDRA IX experiment) and in five dogs exposed to 91 ATA of He-O2 or He-N2-O2. In all cases, the O2 partial pressure was slightly higher than its physiological value. These human and animal studies reveal that elevated pressure of different inert gases did not change the resting heart rate or its respiratory fluctuation. However, the T wave amplitude increased in proportion to the gas density in the three divers; this was also found in four of the five dogs studied. Changes in peak T wave configurations were also observed in the dog experiments. Positional changes in QRS or T vectors cannot explain these T wave changes. 相似文献
76.
Production of vanillic acid from vanillin by resting cells of Serratia marcescens. 总被引:2,自引:2,他引:0 下载免费PDF全文
Resting-cell suspensions of Serratia marcescens were able to convert, quantitatively, 0.3% vanillin to vanillic acid. The vanillic acid-producing activity reached a maximum after 28 h of incubation with 0.01% vanillin as an inducer. 相似文献
77.
Wytske de Vries M. I. H. Aleem Anneke Hemrika-Wagner A. H. Stouthamer 《Archives of microbiology》1977,112(3):271-276
Fumarase-free electron particles from Propionibacterium freudenreichii and P. pentosaceum were prepared by discontinuous sucrose gradient centrifugation, and the influence of 2-n-heptyl-4-hydroxy-quinoline-N-oxide (HQNO) and ultraviolet irradiation on the reduction of menaquinone and cytochrome b with l-lactate or glycerol-3-phosphate and the reoxidation by fumarate was studied. In the presence of HQNO the steady state reduction level of menaquinone during fumarate reduction was increased whereas the steady state reduction level of cytochrome b was decreased as compared with the reduction levels measured in the absence of HQNO. The steady state reduction level of menaquinone during electron transport to fumarate was not influenced by ultraviolet irradiation and the steady state reduction level of cytochrome b was decreased at increasing irradiation times. The data indicate that cytochrome b is involved in the electron transport to fumarate.Abbreviations HQNO
2-n-heptyl-4-hydroxyquinoline-N-oxide
- NQNO
2-n-nonyl-4-hydroxyquinoline-N-oxide
Visiting Professor at the Biological Laboratory 相似文献
78.
The improvement of glass capillary preparation technology has allowed the development of high-resolution and very low-bleeding gas chromatographic columns. Using an all-glass injector and a flame ionization detector, it was possible to get a complete resolution of some of the principal stable oxygenated metabolites of arachidonic acid (cyclized and aliphatic, i.e., eicosanoids). Due to the low bleeding of the column, detector limits exceed those obtained with previously prepared columns. Total profiling studies have been obtained with small amounts of activated washed platelets after only an ether extraction, allowing for the first time a complete, simultaneous survey of cycloxygenase and lipoxygenase pathways. The application has been extended with success to other cell types. 相似文献
79.
80.