全文获取类型
收费全文 | 2342篇 |
免费 | 217篇 |
国内免费 | 2篇 |
出版年
2023年 | 10篇 |
2022年 | 25篇 |
2021年 | 40篇 |
2020年 | 25篇 |
2019年 | 34篇 |
2018年 | 35篇 |
2017年 | 31篇 |
2016年 | 47篇 |
2015年 | 101篇 |
2014年 | 103篇 |
2013年 | 131篇 |
2012年 | 170篇 |
2011年 | 167篇 |
2010年 | 111篇 |
2009年 | 73篇 |
2008年 | 137篇 |
2007年 | 123篇 |
2006年 | 117篇 |
2005年 | 135篇 |
2004年 | 134篇 |
2003年 | 136篇 |
2002年 | 126篇 |
2001年 | 32篇 |
2000年 | 27篇 |
1999年 | 30篇 |
1998年 | 17篇 |
1997年 | 26篇 |
1996年 | 22篇 |
1995年 | 21篇 |
1994年 | 14篇 |
1993年 | 30篇 |
1992年 | 19篇 |
1991年 | 17篇 |
1990年 | 13篇 |
1989年 | 9篇 |
1988年 | 13篇 |
1987年 | 10篇 |
1986年 | 14篇 |
1985年 | 20篇 |
1984年 | 18篇 |
1983年 | 11篇 |
1982年 | 27篇 |
1981年 | 16篇 |
1980年 | 17篇 |
1979年 | 9篇 |
1978年 | 11篇 |
1976年 | 11篇 |
1975年 | 11篇 |
1974年 | 9篇 |
1973年 | 12篇 |
排序方式: 共有2561条查询结果,搜索用时 171 毫秒
11.
John I. Yoder Joe Palys Kevin Alpert Michael Lassner 《Molecular & general genetics : MGG》1988,213(2-3):291-296
Summary As an initial step towards developing a transposon mutagenesis system in tomato, the maize transposable element Ac was transformed into tomato plants via Agrobacterium tumefaciens. Southern analysis of leaf tissue indicated that in nine out of eleven transgenic plants, Ac excised from the T-DNA and reintegrated into new chromosomal locations. The comparison of Ac banding pattern in different leaves of the same primary transformant provided evidnece for transposition during later stages of transgenic plant development. There was no evidence of Ds mobilization in tomato transformants. 相似文献
12.
Effect of Light on the Metabolism of Lipids in the Rat Retina 总被引:1,自引:1,他引:0
Robert E. Anderson Maureen B. Maude Glen A-Wen Pu Joe G. Hollyfield 《Journal of neurochemistry》1985,44(3):773-778
The effect of light on the in vitro incorporation of a variety of radioactive precursors into glycerolipids was tested in isolated retinas of albino rats. There was an increase in the incorporation of [2-3H]myo-inositol, 32Pi, [2-3H]glycerol, and [methyl-3H]choline into retinal phospholipids in light compared to that in darkness. [2-3H]myo-Inositol was incorporated primarily into phosphatidylinositol. 32Pi was incorporated primarily into the phosphoinositides, although there were significant increases in the specific activities of all retinal phospholipids in light compared to those in darkness. Likewise, [2-3H]glycerol incorporation into all retinal phospholipids and diglycerides was greater in light than in the dark. There was no effect of light on the incorporation of [2-3H]ethanolamine into phosphatidylethanolamine or of [3-3H]serine into phosphatidylserine, although these phospholipids were labeled to a greater extent in light with [2-3H]glycerol. There was no effect of light on the incorporation of [3H]palmitic acid into diglycerides and phospholipids, with the exception of phosphatidylinositol. Light also had no effect on the uptake of [2-3H]glycerol, [2-3H]inositol, or [methyl-3H]choline into the retina. We conclude from these studies that light stimulates the phosphoinositide effect in the rat retina. Although some of the results are consistent with a stimulation of de novo synthesis of all lipid classes, our studies with [3H]palmitate, [2-3H]ethanolamine, and [3-3H]serine do not support this conclusion.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
13.
Terry Joe Sprinkle F. Arthur McMorris Jun Yoshino George H. De Vries 《Neurochemical research》1985,10(7):919-931
The relative levels of the central nervous system myelin marker enzyme 2:3-cyclic nucleotide 3-phosphodiesterase (EC 3.1.4.37, CNPase) were determined in neuroblastoma, astrocyte, oligodendrocyte and Schwann cell cultures and in freshly isolated human lymphocytes and platelets. The highest specific activities were associated with the cells that elaborate myelin membrane in the central and peripheral nervous system, oligodendrocytes and Schwann cells, respectively. Antiserum to bovine CNPase recognized both CNP1 and CNP2 in CNS myelin and human oligodendroglioma. In addition, a 53,000 dalton protein was evident on autoradiographs of immunoblotted PNS myelin and human oligodendroglioma proteins. Cultured rat oligodendrocyte, C6 and mouse NA neuroblastoma CNPase appear to share common determinants with the corresponding normal rat CNS enzyme. 相似文献
14.
Human lymphocytes which were non-mitogen-stimulated, and which were depleted of lipoproteins, were found to be deficient in DNA excision repair typically initiated in these cells in response to treatment with a direct-acting polynuclear aromatic hydrocarbon carcinogen. Lymphocytes either depleted of lipoproteins or supplemented with human low-density lipoproteins formed DNA-carcinogen adducts which were not chromatographically distinguishable. The state of lipoprotein depletion did not alter lymphocyte uptake of thymidine from the medium. Lymphocytes which were depleted of lipoproteins, treated with carcinogen, and subsequently supplemented with low-density lipoproteins, regained the ability to engage in DNA excision repair. The data suggest that either low-density lipoprotein(s), or a component(s) of low-density lipoprotein(s), is required by human lymphocytes in order to initiate excision repair of carcinogen-damaged DNA. 相似文献
15.
Norma L. Trolinder Jerry D. Berlin Joe R. Goodin 《In vitro cellular & developmental biology. Plant》1987,23(11):789-794
Summary A cotton cell suspension culture has been developed that provides unique opportunities for plant biologists to investigate
early developmental events regulating cotton fiber properties, plant cell elongation, and cell wall biogenesis. The suspension
culture was derived from cells of cotton (Gossypium hirsutum L.) ovule callus. These cells undergo the stages of fiber development
previously described for in vivo fiber development. Fibers range in length up to 11 mm and have secondary walls.
Supported by the U.S. Department of Agriculture, Agricultural Research Service, Southern Regional Research Laboratory, New
Orleans, Louisiana, and Cotton Incorporated, Raleigh, North Carolina. 相似文献
16.
Dielectrophoresis, the motion produced by the action of nonuniform electric field upon a neutral object, is shown to be a simple and useful technique for the study of cellular organisms. In the present study of yeast (Saccharomyces cerevisiae) using a simple pin-pin electrode system of platinum and high-frequency alternating fields, one observes that the collectability of cells at the electrode tip, i.e. at the region of highest field strength, depends upon physical parameters such as field strength, field uniformity, frequency, cell concentration, suspension conductivity, and time of collection. The yield of cells collected is also observed to depend upon biological factors such as colony age, thermal treatment of the cells, and chemical poisons, but not upon irradiation with ultraviolet light. Several interesting side effect phenomena coincident with nonuniform electric field conditions were observed, including stirring (related to “jet” effects at localized electrode sites), discontinuous repulsions, and cellular rotation which was found to be frequency dependent. 相似文献
17.
Summary Kinetic studies of the uptake of hydroquinone--D-glucoside (arbutin) by excised roots of barley demonstrated that this compound is actively transported. Similar studies on the uptake of hydroquinone indicated that the latter compound enters the root tissues by diffusion. A concentration gradient favouring diffusion is maintained for at least three hours by the conversion of the aglucone to its correspondings glucoside. Hydroquinone, at a concentration of 5 mM, reduced uptake of 86rubidium ion by approximately 30%.This work was supported by a grant from the National Research. Council of Canada 相似文献
18.
Hormonal Regulation of Cell Elongation in the Hypocotyl of Rootless Soybean: An Evaluation of the Role of DNA Synthesis 总被引:7,自引:6,他引:1
下载免费PDF全文
![点击此处可从《Plant physiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
A method was developed where soybean seedlings were grown without roots to study the influence of hormones of root origin on shoot growth. Excision of the root resulted in inhibition of apical section growth and DNA synthesis and inhibited elongating section growth. A synthetic cytokinin restored DNA synthesis in the apical section, but did not influence growth in either the apical or elongating sections. Low concentrations of gibberellin with the cytokinin restored growth in the apical section. Gibberellin alone was sufficient to restore growth in the elongating section.An inhibitor of DNA synthesis, 5-fluorodeoxyuridine, inhibited the increase in apical section DNA without inhibiting control or gibberellin-induced growth in the elongating section. Experiments with (14)C-thymidine resulted in no DNA labeling differences in the elongating section under conditions where gibberellin-induced elongation varied from 50% to 73% above controls. It was concluded that gibberellin-induced elongation in soybean hypocotyl occurred in the absence of DNA synthesis. Gibberellin does stimulate DNA synthesis in the apical tissue apart from its effect on cell elongation.Excised soybean hypocotyl elongated maximally at 10(-6)m auxin. At higher auxin concentrations, fresh weight and ethylene production increased, but elongation was reduced. Addition of GA to the higher auxin concentrations resulted in a 50% inhibition in auxin-induced ethylene production and resumption in maximal elongation. Added ethylene inhibited elongation 30% at 2 mul/l. Addition of up to 100 mul/l ethylene did not inhibit elongation with GA present in the incubation medium. Thus GA may counteract ehtylene inhibition of cell elongation in addition to inhibiting ethylene production in auxin-treated tissues. 相似文献
19.
B12 Coenzyme-dependent Ribonucleotide Reductase in Rhizobium Species and the Effects of Cobalt Deficiency on the Activity of the Enzyme 总被引:6,自引:2,他引:4
下载免费PDF全文
![点击此处可从《Journal of bacteriology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
This investigation revealed that the ribonucleotide reductases in extracts of Rhizobium leguminosarum, R. trifolii, R. phaseoli, R. japonicum, and R. meliloti 3DOal (ineffective in nitrogen fixation) are dependent upon B(12) coenzyme for activity. Rhizobium and certain Lactobacillus species are the only two groups of organisms known to contain B(12) coenzyme-dependent ribonucleotide reductases. Extracts of cobalt-deficient R. meliloti cells assayed in the presence of optimum B(12) coenzyme showed a 5- to 10-fold greater ribonucleotide reductase activity than comparable extracts from cells grown on a complete medium. Furthermore, cobalt-deficient cells were abnormally elongated and contained reduced contents of deoxyribonucleic acid. The addition of purified deoxyribonucleosides to cobalt-deficient cultures of R. meliloti failed to alleviate deficiency symptoms. 相似文献
20.