全文获取类型
收费全文 | 15036篇 |
免费 | 949篇 |
国内免费 | 6篇 |
专业分类
15991篇 |
出版年
2022年 | 79篇 |
2021年 | 154篇 |
2020年 | 68篇 |
2019年 | 109篇 |
2018年 | 161篇 |
2017年 | 153篇 |
2016年 | 245篇 |
2015年 | 365篇 |
2014年 | 443篇 |
2013年 | 1144篇 |
2012年 | 707篇 |
2011年 | 820篇 |
2010年 | 510篇 |
2009年 | 502篇 |
2008年 | 782篇 |
2007年 | 816篇 |
2006年 | 800篇 |
2005年 | 808篇 |
2004年 | 823篇 |
2003年 | 769篇 |
2002年 | 780篇 |
2001年 | 384篇 |
2000年 | 363篇 |
1999年 | 349篇 |
1998年 | 230篇 |
1997年 | 172篇 |
1996年 | 159篇 |
1995年 | 150篇 |
1994年 | 131篇 |
1993年 | 177篇 |
1992年 | 220篇 |
1991年 | 198篇 |
1990年 | 180篇 |
1989年 | 182篇 |
1988年 | 162篇 |
1987年 | 176篇 |
1986年 | 146篇 |
1985年 | 134篇 |
1984年 | 128篇 |
1983年 | 79篇 |
1982年 | 119篇 |
1981年 | 101篇 |
1980年 | 83篇 |
1979年 | 84篇 |
1978年 | 89篇 |
1977年 | 81篇 |
1974年 | 70篇 |
1973年 | 81篇 |
1972年 | 58篇 |
1969年 | 59篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
Optimum conditions for electric pulse-mediated gene transfer to mammalian cells in suspension 总被引:5,自引:0,他引:5
H Hama-Inaba M Takahashi M Kasai T Shiomi A Ito F Hanaoka K Sato 《Cell structure and function》1987,12(2):173-180
A pulse-generating machine which delivers exponentially decaying pulses over broad range of pulse lengths was used to determine the optimum pulse conditions for gene transfer to FM3A cells. In the transformation of tk- cells with pTK1, a single pulse of 100-2000 microseconds gave a high transformation frequency at 1.5-6 kV/cm and room temperature, the highest transformation frequency obtained being 3 X 10(-3). As the suspension buffer for cells exposed to the pulse, Saline G was better than PBS(-) for obtaining a large number of transformants because it ensured high cell viability. 相似文献
22.
Phylogenetic systematics of the nymphaeales 总被引:2,自引:0,他引:2
Motomi Ito 《Journal of plant research》1987,100(1):17-35
A cladistic analysis was applied to reveal the phylogenetic relationships among the Nymphaeales. Seventeen out of twenty three
characters in gross morphology, anatomy and palynology were analyzed, for their evolutionary polarities. From the results
of the present analysis, the phylogenetic status of each genus and their relationships were clarified: 1)Nelumbo is a distinct taxon and is presumed to have originated from an ancestral stock of the Nymphaeales; 2)Ceratophyllum has a close phylogenetic relationship withCabomba; and 3) in the Nymphaeaceaesensu stricto, Nuphar and the remaining genral constitute a monophyletic group.
A conclusion obtained from the present analysis was that the following three families should be recognized in the Nymphaeales;
Nelumbonaceae Nymphaeaceae, and Ceratophyllaceae. The generaBrasenia andCabomba are traditionally classified in the Nymphaeaceae or in the independent family Cabombaceae. However, they should be included
in the family Ceratophyllaceae. 相似文献
23.
We have identified DNA fragments which bind specifically to the nuclear matrix in vitro, termed matrix association regions (MARs), in the first and fourth introns of rat alpha 2-macroglobulin gene. The MAR in the first intron is enriched with sequences closely related to the cleavage consensus of topoisomerase II, and contains the binding site of nuclear factor-alpha, a sequence-specific DNA binding protein reported previously. 相似文献
24.
A radioimmunoassay for human pro-luteinizing hormone-releasing factor [pro-LRF(14-69)OH] 总被引:1,自引:0,他引:1
A Motoyama I Wakabayashi S Minami H Sugihara F Takahashi S Akira N Ling 《Endocrinologia japonica》1987,34(1):133-137
A radioimmunoassay (RIA) for human pro-LRF(14-69)OH was developed with an antiserum, generated in a rabbit, to [Tyr67]pro-LRF(47-67)NH2 conjugated to BSA. This antiserum bound 28-32% of [125I]pro-LRF(14-69)OH at a final dilution of 1:2500 and the binding was inhibited by pro-LRF(14-69)OH in a dose-dependent manner. The sensitivity of the RIA was 31.2-62.5 pg and the dose that inhibited 50% of the binding to the tracer was 280-320 pg. Intra- and inter-assay coefficients of variation at 50% inhibition were 8 and 12%, respectively. Neither LRF nor pro-LRF(14-37)OH was recognized by the antiserum. The dilution curve generated with human hypothalamic extract was parallel to that of pro-LRF(14-69)OH. In addition the extract yielded a major immunoreactive peak emerging in elution volumes concordant with [125I]pro-LRF(14-69)OH on Sephadex G-50 chromatography. 相似文献
25.
Katsuya Koike Masato Mori Yukishige Ito Yoshiaki Nakahara Tomoya Ogawa 《Glycoconjugate journal》1987,4(2):109-116
The first total synthesis of glycosphingolipids isolated from wheat flour has been achieved in a regio- and stereo-controlled manner.Abbreviations THF
tetrahydrofuran
- DMF
dimethylformamide
Part 53 in the series Synthetic Studies on Cell Surface Glycans 相似文献
26.
Orosomucoid (ORM) typing by isoelectric focusing: evidence for gene duplication of ORM1 and genetic polymorphism of ORM2 总被引:2,自引:0,他引:2
Summary It has been demonstrated that the genetic polymorphism of human serum orosomucoid (ORM) is controlled by polymorphic ORM1
and monomorphic ORM2 loci. In this study a Japanese family was encountered in which several members had puzzling electrophoretic
patterns consisting of four bands. The ORM patterns were due to the products of a duplicated ORM1 locus haplotype (ORM1
*
2·1) or the products of new variant alleles at the ORM2 locus. The ORM1
*
2·1 haplotype is very common in the Japanese population, occurring at an allele frequency of 0.16. The increased occurrence of
ORM1 2-1 and the heterogeneity in band intensity among ORM1 2-1 phenotypes could be explained in terms of a duplicated gene
ORM1
*
2·1. The ORM2 locus proved to be polymorphic, with six alleles in the Japanese population.
Dedicated to Professor Dr. K. Nishigami on the occasion of his 60th birthday 相似文献
27.
Komatsuna (Brassica campestris L. var. rapa) plants were grownhydroponically under various conditions with respect to thesupply of nitrate, and the variations in levels of natural 15Nabundance (15N) in nitrogenous fractions of leaf blades, petiolesplus midribs, and roots in these plants were analyzed. The fractionation of nitrogen isotopes during uptake of nitratewas null irrespective of the concentrations of nitrate in theculture medium. The roots had lower 15N values than that inthe nitrate applied to plants. The nitrate in the three tissuesexamined had higher 15N values than that in the nitrate applied:the values were highest in the leaf blades which were presumedto have highest activities in terms of reduction of nitrate.In contrast, the amino acids and residual fractions had lower15N values than those in the nitrate applied. These resultssuggest that reduction of nitrate is a critical step in thefractionation of nitrogen isotopes in plant tissues in vivo.
1Permanent address: Fukuoka Agricultural Experiment Station,Yoshiki 587, Chikushino, 818 Japan. (Received March 10, 1989; Accepted July 10, 1989) 相似文献
28.
Quantitative Analysis of Endogenous Gibberellins in Normal and Dwarf Cultivars of Rice 总被引:7,自引:0,他引:7
Kobayashi Masatomo; Sakurai Akira; Saka Hitoshi; Takahashi Nobutaka 《Plant & cell physiology》1989,30(7):963-969
Endogenous levels of gibberellins in shoots and ears of twodwarf rice (Oryza sativa L.) cultivars, Tan-ginbozu (dx mutant)and Waito-C (dy mutant), were analyzed and compared with thoseof normal rice cultivar, Nihonbare. The endogenous levels of13-hydroxylated gibberellins in Tan-ginbozu were much lowerthan those in Nihonbare. In Waito-C, the levels of GA19 andGA20 in the shoots were higher but that of GA1 was lower thanthe levels of these gibberellins in Nihonbare. These resultssupport the hypothesis that the dy gene controls the 3ß-hydroxylationof GA20 to GA1 while the dx gene controls a much earlier stepin the gibberellin biosynthesis. Our results indicate that GA1is the active gibberellin that regulates the vegetative growthof rice. The endogenous levels of GA4 in the ears of the twodwarf cultivars of rice were higher than the level of GA4 inthe ears of the normal cultivar, Nihonbare suggesting that thebiosynthesis of gibberellin is not blocked in the anthers ofthe dwarf rice. (Received April 27, 1989; Accepted July 12, 1989) 相似文献
29.
Correction of congenital microtia using the tissue expander 总被引:6,自引:0,他引:6
Y Hata K Hosokawa K Yano K Matsuka O Ito 《Plastic and reconstructive surgery》1989,84(5):741-51; discussion 752-3
We attempted auricular reconstruction using Radovan-type inflatable silicone expanders in six children and one adult, with the complete hypoplastic, the conchal remnant, and constricted type of microtia. Ear frameworks, including the helix, anthelix, concha, and tragus, were prepared using autologous rib cartilage. Based on the surface area of the normal adult auricle, the silicone expander was tentatively shaped and sized into a rotated semiellipse and expanded with 70 cc saline. Auricular reconstruction on the framework was completed at the time of insertion in four of the seven patients, requiring no elevation of the ear. The reconstructed auricle was satisfactory in both color and texture and had nearly normal sensation. Mild complications were noted in three of the seven patients. However, no resorption of the inserted rib cartilage has been observed 14 months to 2 years and 5 months after the operation. Slight shrinkage of the expanded skin was noted in each patient. 相似文献
30.
The changes in monoamine levels of different brain regions following Japanese encephalitis virus (JEV) intraperitoneal inoculation were examined in experimentally JEV-infected mice. In addition, virus distribution was studied using infectivity assay and immuno-histochemistry of viral antigen. 1) The level of monoamines in brain tissues was not affected by 48 hours after viral inoculation, but marked effects were elicited at 96 hours after the inoculation. The cerebral concentration of 5-hydroxyindole-3-acetic acid (5 HIAA) was increased, while that of dopamine (DA) showed a decrease. Especially these alteration were observed in the cerebral cortex, but not in the cerebellum. 2) The viral growth in the brain was observed at 48 hours after the inoculation. The growth in the cerebellum, however, was found to be lower than those in other cerebral regions. 3) The viral antigen was detected in the cerebral cortex, hippocampus, mesencephalon and diencephalon in addition to the substantia nigra and striatum. From these results, it is presumed that clinical manifestation of JEV infection may involve the changes in the metabolism of neurotransmitter, especially those of DA and serotonin in the brain. 相似文献