全文获取类型
收费全文 | 6372篇 |
免费 | 597篇 |
国内免费 | 3篇 |
出版年
2023年 | 28篇 |
2022年 | 63篇 |
2021年 | 124篇 |
2020年 | 68篇 |
2019年 | 85篇 |
2018年 | 109篇 |
2017年 | 100篇 |
2016年 | 162篇 |
2015年 | 277篇 |
2014年 | 320篇 |
2013年 | 412篇 |
2012年 | 435篇 |
2011年 | 478篇 |
2010年 | 286篇 |
2009年 | 267篇 |
2008年 | 395篇 |
2007年 | 381篇 |
2006年 | 317篇 |
2005年 | 338篇 |
2004年 | 314篇 |
2003年 | 318篇 |
2002年 | 312篇 |
2001年 | 52篇 |
2000年 | 32篇 |
1999年 | 52篇 |
1998年 | 76篇 |
1997年 | 49篇 |
1996年 | 54篇 |
1995年 | 39篇 |
1994年 | 46篇 |
1993年 | 51篇 |
1992年 | 39篇 |
1991年 | 34篇 |
1990年 | 28篇 |
1989年 | 32篇 |
1988年 | 23篇 |
1987年 | 34篇 |
1984年 | 22篇 |
1983年 | 29篇 |
1982年 | 39篇 |
1981年 | 27篇 |
1980年 | 27篇 |
1979年 | 33篇 |
1978年 | 30篇 |
1977年 | 22篇 |
1974年 | 27篇 |
1973年 | 22篇 |
1972年 | 27篇 |
1970年 | 22篇 |
1967年 | 28篇 |
排序方式: 共有6972条查询结果,搜索用时 31 毫秒
81.
David Kipling Helen E. Wilson Arthur R. Mitchell Benjamin A. Taylor Howard J. Cooke 《Chromosoma》1994,103(1):46-55
Cytologically, the centromere is found at the very end of most Mus musculus chromosomes, co-localizing with an array of minor satellite sequences. It is separated from the euchromatin of the long arm by a large domain of heterochromatin, composed in part of arrays of major satellite sequences. We used oligonucleotide probes that specifically detect regions of sequence variation found in certain cloned minor satellite sequences. They detect a limited subset of the minor satellite arrays in the mouse genome, based on both pulsed-field gel electrophoresis and in situ hybridization data, and provide direct molecular genetic markers for individual centromeres in some inbred mouse strains. Array size polymorphisms detected by these probes map to positions consisten with the centromeres of chromosomes 1 and 14 in the BXD recombinant inbred (RI) strains. The genetic distances between these minor satellite arrays and loci on the long arms of chromosomes 1 and 14 are consistent with repression of meiotic recombination in the heterochromatic domains separating them. The existence of chromosome-specific minor satellite sequences implies that the rate of sequence exchange between non-homologous chromosomes relative to the rate between homologous chromosomes is much lower than has previously been postulated. We suggest that the high degree of sequence homogeneity of mouse satellite sequences may instead reflect recent common ancestry. 相似文献
82.
In this study we examined the biosynthesis of abscisic acid (ABA) by developing corn (Zea mays L.) embryos. Three comparisons were made: ABA biosynthesis in embryos isolated from kernels grown in vitro with those grown in the field; the developmental profile of ABA content with that of biosynthesis; and ABA biosynthesis in corn embryos lacking carotenoid precursors with ABA biosynthesis in normal embryos. Embryos were harvested at various times during seed development and divided into two groups. Endogenous levels of ABA were measured in one group of embryos and ABA biosynthetic capacity was measured in the other group. The ABA biosynthetic capacity was measured with and without tetcyclacis (an inhibitor of ABA degradation) in embryos from both field-grown and in-vitro-grown corn kernels. Reduced-carotenoid (either fluridone-treated or genetically viviparous) embryos were also included in the study. Corn kernels developing under field and in-vitro conditions differed from each other in their responses to tetcyclacis and in their profiles of ABA biosynthesis during development. Therefore, in-vitro kernel culture may not be an appropriate substitute for field conditions for studies of embryo development. The developmental profiles of endogenous ABA content differed from those of ABA biosynthesis in isolated embryos of both in-vitro-and field-grown kernels. This indicated that ABA levels in the developing embryos were determined by import from the maternal tissues available to the embryos rather than by in-situ biosynthesis. In embryos with reduced levels of carotenoids, either fluridone-treated or genetically viviparous embryos, ABA biosynthesis was low or nonexistent. This result is expected for the presence of an indirect pathway of ABA biosynthesis and in the absence of ABA precursors.Abbreviations ABA
abscisic acid
- DAP
days after pollination 相似文献
83.
Abscisic acid (ABA) inhibited embryogenesis in anther culture of Brussels sprouts. This was accompanied by enhanced ethylene production during the first half of the anther culture period followed by a reduction in ethylene during the latter half, when compared to anthers not treated with ABA. The enhancement of ethylene production by ABA 6 h and 48 h after the start of the culture period was counteracted by the ethylene biosynthesis inhibitor aminoethoxyvinylglycine (AVG). Both AVG and the ethylene antagonist AgNO3 removed much of the ABA inhibition of embryogenesis, suggesting that at least part of the ABA effect on embryo production is mediated through increased ethylene biosynthesis.
ABA promotion of ethylene production was reduced by high temperature: less ethylene evolved from ABA-treated anthers following a 24 h treatment at 35°C than from ABA-treated anthers incubated continuously at 25°C. A high temperature treatment such as this is invariably necessary for embryogenesis in Brussels sprouts anther culture. 相似文献
ABA promotion of ethylene production was reduced by high temperature: less ethylene evolved from ABA-treated anthers following a 24 h treatment at 35°C than from ABA-treated anthers incubated continuously at 25°C. A high temperature treatment such as this is invariably necessary for embryogenesis in Brussels sprouts anther culture. 相似文献
84.
Cheryl D. Helgason Lianfa Shi Arnold H. Greenberg Yufang Shi Peter Bromley Thomas G. Cotter Douglas R. Green R. Chris Bleackley 《Experimental cell research》1993,206(2)
Cytotoxic T lymphocyte (CTL)-mediated lysis is accompanied by fragmentation of target cell DNA into an oligonucleosome ladder, a hallmark of apoptosis. Is this a fortuitous coincidence, or could CTL be inducing lysis by activation of the suicide signal? In this report we demonstrate that CTL-mediated target cell death can be blocked with the drug aurintricarboxylic acid (ATA). The abrogation of death correlates with the inhibition of DNA fragmentation. While ATA prevented DNA fragmentation, it failed to significantly alter protein, RNA, or DNA synthesis in the cell lines over the dose range used. In addition, there was no inhibition of cell-cell interaction or granule exocytosis during CTL-mediated killing. ATA also significantly inhibited the cytolysis and DNA fragmentation mediated by isolated cytolytic granules, as well as the granular protein fragmentin. We developed an assay in which target cells could be separated from CTL after binding and programming for lysis. Once they had received the "kiss of death," target cells could be rescued from lysis (as indicated by inhibition of DNA fragmentation and increased target cell viability) by treatment with ATA. These results suggest that ATA blocks target cell death by inhibition of DNA fragmentation, and further, that chromatin degradation is a cause rather than a result of cell death in CTL-mediated lysis. 相似文献
85.
Susanne Popp Anna Jauch Detlev Schindler Michael R. Speicher Christoph Lengauer Helen Donis-Keller Harold C. Riethman Thomas Cremer 《Human genetics》1993,92(6):527-532
The identification of marker chromosomes in clinical and tumor cytogenetics by chromosome banding analysis can create problems. In this study, we present a strategy to define minute chromosomal rearrangements by multicolor fluorescence in situ hybridization (FISH) with whole chromosome painting probes derived from chromosome-specific DNA libraries and Alu-polymerase chain reaction (PCR) products of various region-specific yeast artificial chromosome (YAC) clones. To demonstrate the usefulness of this strategy for the characterization of chromosome rearrangements unidentifiable by banding techniques, an 8p+ marker chromosome with two extra bands present in the karyotype of a child with multiple anomalies, malformations, and severe mental retardation was investigated. A series of seven-color FISH experiments with sets of fluorochrome-labeled DNA library probes from flow-sorted chromosomes demonstrated that the additional segment on 8p+ was derived from chromosome 6. For a more detailed characterization of the marker chromosome, three-color FISH experiments with library probes specific to chromosomes 6 and 8 were performed in combination with newly established telomeric and subtelomeric YAC clones from 6q25, 6p23, and 8p23. These experiments demonstrated a trisomy 6pter6p22 and a monosomy 8pter8p23 in the patient. The present limitations for a broad application of this strategy and its possible improvements are discussed.Dedicated to Professor Dr. U. Wolf on the occasion of his 60th birthday 相似文献
86.
Paul G. McGuire Helen M. Walker-Caprioglio Sally A. Little Linda J. McGuffee 《In vitro cellular & developmental biology. Animal》1993,29(2):135-139
Summary The structure and function of vascular smooth muscle cells have been extensively investigated with the aid of in vitro culture
techniques. The majority of studies have utilized aortic tissue as the source of cells. We present here a method for isolating
and culturing smooth muscle cells of the rat superior mesenteric artery, an elasto-muscular vessel that is structurally and
functionally different from the aorta. Cells were isolated from partially digested explants and characterized by immunochemical
and biochemical techniques. Unlike cultured fibroblasts, the cultured cells stained positive for smooth muscle specific actin.
The cells also produced laminin and type IV collagen in culture. This method provides a means for the isolation of large numbers
of viable smooth muscle cells from the superior mesenteric artery which can be propagated in culture for in vitro study. 相似文献
87.
Carton W. Chen Tin-Wein Yu † Yi-Shing Lin Helen M. Kieser David A. Hopwood 《Molecular microbiology》1993,7(6):925-932
The SLP2 plasmid had previously been demonstrated genetically to exist In Streptomyces lividans by its ability to promote conjugation and to elicit‘pocks’on recipient (SLP2?) cultures, but it had not been physically detected. Using pulsed-field gel electrophoresis, a 50kb linear DNA was isolated from SLP2+ but not SLP2? strains of S. lividans, and from Streptomyces coelicolor and Streptomyces parvulus strains to which SLP2 had been transferred by conjugation or transformation. We conclude that this linear DNA is SLP2. The terminal fragments of SLP2 were cloned. The determined sequences revealed a 44 bp imperfect terminal inverted repeat. The terminal 12 bp sequence of SLP2 was identical to those of two other Streptomyces linear plasmids, pSLA2 and pSCL, and similar to the terminal sequences of another Streptomyces linear plasmid, SCP1. The termini of SLP2 DNA were resistant to digestion by λ exonuclease and ExoIII. A truncated (probably crippled) copy of Tn4811 is present on the plasmid. While the SLP2 plasmid exists as a tree form in the host, a 15.7 kb sequence corresponding to the segment of SLP2 from Tn4811 to the right terminus is also present (at a copy number similar to the free form) elsewhere in the genome of S. lividans. Furthermore, SLP2 is partially homologous to a newly discovered 650 kb linear plasmid in S. parvulus. 相似文献
88.
Michael A. Poss Joyce A. Reid Charles A. Free W. Lynn Rogers Helen Weber Denis E. Ryono Tamara Dejneka Jack M. DeForrest Thomas L. Waldron Russell J. Brittain Harold N. Weller Maria P. Cimarusti Edward W. Petrillo 《Bioorganic & medicinal chemistry letters》1993,3(12):2739-2744
The syntheses and pharmacological activity of a series of diol sulfonamides which function as inhibitors of human renin are described. The most potent compound in this series, compound 20 (SQ 33,800), is a subnanomolar inhibitor of human renin (IC50 = 0.35 × 10−9 M). 相似文献
89.
Helen E. O'connor David R. Stevens Stuart V. Ruffle Jonathan H. A. Nugent Saul Purton 《Plant Molecular Biology Reporter》1993,11(3):207-211
The isolation of chloroplast DNA fromChlamydomonas reinhardtii requires the efficient separation of this AT-rich genome from the GC-rich nuclear genome by density-gradient centrifugation.
We describe a simple and efficient method for separating these DNA fractions by using a sodium iodide gradient in combination
with the DNA-binding dye, bisbenzimide. The yield of chloroplast DNA is close to the theoretical maximum and the DNA is suitable
for restriction enzyme analysis and cloning. This method is applicable to the isolation of AT-rich plastid genomes from other
organisms and may be appropriate as a general method for separating species of DNA that differ in their AT/GC ratios.
An erratum to this article is available at . 相似文献
90.
An in vitro test method for general metal toxicity screening was designed, based on the cellular response to stress. The expression of a transfected human growth hormone gene sequence driven by the human heat-shock protein 70 promoter in NIH/3T3 cells was used as marker of noxious contact with metal compounds. Out of a series of31 metals, 17 were competentfor inducing this stress response system. According to the effective concentration and to the intensity of the response, three different clusters of positive compounds emerged and were ranked as strong, intermediate strength and weak inducers. These results correlated well with data from other in vivo and in vitro metal toxicity studies, including LD50 in mice. Apparently the positivelnegative compounds also fitted well with data from genotoxicity and carcinogenesis studies on metal salts.Abbreviations hGH
human growth hormone
- hsp70
70 kDa heat-shock protein 相似文献