全文获取类型
收费全文 | 20666篇 |
免费 | 1743篇 |
国内免费 | 61篇 |
专业分类
22470篇 |
出版年
2022年 | 152篇 |
2021年 | 239篇 |
2020年 | 141篇 |
2019年 | 199篇 |
2018年 | 242篇 |
2017年 | 200篇 |
2016年 | 339篇 |
2015年 | 624篇 |
2014年 | 674篇 |
2013年 | 1035篇 |
2012年 | 1135篇 |
2011年 | 1169篇 |
2010年 | 717篇 |
2009年 | 681篇 |
2008年 | 1068篇 |
2007年 | 1105篇 |
2006年 | 1015篇 |
2005年 | 1016篇 |
2004年 | 949篇 |
2003年 | 935篇 |
2002年 | 908篇 |
2001年 | 224篇 |
2000年 | 183篇 |
1999年 | 262篇 |
1998年 | 266篇 |
1997年 | 194篇 |
1996年 | 208篇 |
1995年 | 182篇 |
1994年 | 198篇 |
1993年 | 166篇 |
1992年 | 179篇 |
1991年 | 168篇 |
1990年 | 145篇 |
1989年 | 156篇 |
1988年 | 172篇 |
1987年 | 158篇 |
1986年 | 147篇 |
1985年 | 183篇 |
1984年 | 199篇 |
1983年 | 189篇 |
1982年 | 205篇 |
1981年 | 239篇 |
1980年 | 207篇 |
1979年 | 163篇 |
1978年 | 191篇 |
1977年 | 169篇 |
1976年 | 141篇 |
1975年 | 146篇 |
1974年 | 164篇 |
1973年 | 161篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
George Lymberopoulos John N. Hawthorne 《Biochimica et Biophysica Acta (BBA)/Molecular Cell Research》1984,805(3):285-290
Pig platelet phosphoinositides have been labelled with [3H]inositol and then treated with thrombin in the absence of Ca2+. There was a loss of labelled phosphatidylinositol 4,5-bisphosphate between 30 and 60 s after the addition of thrombin but the general picture was of increased labelling over a 4-min period. Labelling of phosphatidylinositol 4-phosphate showed no period of loss but there was an early loss of phosphatidylinositol and no increased labelling during the 4-min incubation. The small amount of lysophosphatidyl[3H]inositol in the platelets was not affected by thrombin treatment. Thrombin caused loss of [14C]arachidonate-labelled phosphatidylcholine, phosphatidylethanolamine and phosphatidylinositol. 相似文献
122.
A method for the estimation of chlorophyll turnover in wheat leaves is presented. This is based on the inhibition of chlorophyll synthesis by treatment of the cut leaves with laevulinic acid (LA), a competitive inhibitor of δ-aminolaevulinic acid dehydratase. The turnover of chlorophyll in young, greening leaves, given short periods of light was a relatively rapid process. However, in seedlings exposed to light for longer periods the turnover became progressively slower, and was measured in days rather than hours. 相似文献
123.
Fractionation of several type II specific restriction endonucleases was achieved by separation on two novel biospecific matrices. The matrices are pyran, a copolymer of divinyl ether of maleic anhydride, and Cibacron Blue F3GA, a blue dye commonly used for the calibration of molecular sieves. Both compounds are insolubilized by coupling to sepharose through a cyanogen bromide linkage and in their soluble form inhibit the restriction endonucleases which we have tested. These affinity matrices can be used to obtain restriction endonucleases from crude extracts after removal of nucleic acids. They have also proven to have a high capacity when used as subsequent steps in enzyme purification. Their additional advantage is the rapid development time and reusability of columns packed with the two matrices. 相似文献
124.
A Kappas N Shinagawa Y Arabi H Thompson D Burdon F Dimock R H George J Alexander-Williams M R Keighley 《BMJ (Clinical research ed.)》1978,1(6114):675-678
Twenty-eight patients with histologically proved pseudomembranous colitis have been seen in one hospital since July 1975. All patients with the disease had received antibiotics, six for infections not requiring operations; the other 22 cases all occurred after major surgery. All the patients had diarrhoea; six patients also had fever with clinical signs of sepsis, and three had abdominal pain thought to be due to anastomotic dehiscence after colonic resection. Pseudomembranous colitis was associated with white blood counts over 15 000/mm3 in 17 patients and albumin concentrations of less than 30 g/1 in 18. Pseudomembranous colitis was an incidental finding at necropsy in two of six patients who had not had an operation. Of the 22 patients who had had major surgery, nine died from this complication; in all except two of these cases the diagnosis was made only at necropsy. If pseudomembranous colitis is suspected on clinical grounds or if there is an unexplained complication after colorectal surgery repeat sigmoidoscopy and testing for faecal toxins should be carried out to establish the diagnosis so that prompt supportive treatment can be given. 相似文献
125.
126.
Quinaldine sulphate is demonstrated in this study to be a convenient and safe anaesthetic for use with tropical marine fishes. Both onset of anaesthesia and recovery are significantly more rapid than with the parent compound, quinaldine. 相似文献
127.
A procedure is described which is capable of detecting the changes in size and/or density of small membrane vesicles resulting from solute uptake. Vesicles which have taken up solute sediment more slowly in a density gradient, the ratio of glycine uptake/vesicle-trapped space is not uniform in the vesicle population, and vesicles with higher uptake/space ratios are preferentially retarded upon centrifugation.Alanine transport activity is associated with glycine transport activity in that retardation of vesicles due to glycine uptake equally retards vesicles possessing alanine uptake activity. 相似文献
128.
A silver ion-loaded microparticulate cation-exchange resin column has been used for high-performance liquid chromatographic (HPLC) separation of the p-nitrophenacyl esters of several series of closely related prostaglandins: 8-iso-PGE2, 11-epi-PGE2, 5-trans-PGE2, PGE2, PGF1α, PGE1, and PGF2α, PGA2 and PGB2; 15 (R)-methyl-PGE2 and 15 (S)-methyl-PGE2; 5-trans-PGA2 and PGA2; and 5-trans-PGF2α and PGF2α. The properties of this column are compared with those of silica-gel and reversed-phase columns. 相似文献
129.
Summary We examined the role of subterranean termites in decomposition of cattle dung, various herbaceous plant species and wood in a Chihuahuan desert ecosystem. From July–September, termites removed dung at a rate of 0.63 g day-1 accounting for a percent mass loss of 19.5–100%. During the autumn subterranean termites consumed more than 50% of the leaves of the shrub Larrea tridentata, the grass Erioneuron pulchellum and annual plant Lepidium lasiocarpum and Baileya multiradiata but used very little of two other annuals Eriastrum diffusum and Eriogonum trichopes. Yucca inflorescence stalks on plots with termites lost 23% of their original mass in 30 months while those on termite free soils lost 11%. Elimination of termites resulted in reduction of fluff grass, Erioneuron pulchellum biomass, thereby affecting the structure of the ecosystem. 相似文献
130.
George J. P. Murphy 《Planta》1980,149(5):417-426
Naphthalene-1-acetic acid (NAA) binding by membrane fractions derived from maize has been re-evaluated. Using a computer curve-fitting procedure only one major type of NAA binding, in terms of binding affinity, could be identified. Auxins, antiauxins and structurally related compounds have been tested for their competitive effect on NAA binding and the inhibitor constants for a number of these have been determined. Extracts from various plant species have been examined for their NAA binding ability, but all showed much less binding than maize leaf or coleoptile preparations. The possibility of the NAA binding by maize extracts being due to a true hormone receptor is discussed.Abbreviations BA
benzoic acid
- CPIB
p-chlorophenoxyisobutyric acid
- 2,4-D
2,4-dichlorophenoxyacetic acid
- DCB
2,4-dichlorobenzoic acid
- IAA
indolyl-3-acetic acid
- NAA
napthalene-1-acetic acid
- 2-NAA
napthalene-2-acetic acid
- NAOA
napthalene-2-oxyacetic acid
- PA
phenylacetic acid
- PU
phenylurea
- 2,4,5-T
2,4,5-trichlorophenoxyacetic acid
- TIBA
2,3,5-triiodobenzoic acid 相似文献