全文获取类型
收费全文 | 2887篇 |
免费 | 98篇 |
国内免费 | 69篇 |
出版年
2023年 | 15篇 |
2022年 | 28篇 |
2021年 | 44篇 |
2020年 | 40篇 |
2019年 | 58篇 |
2018年 | 49篇 |
2017年 | 77篇 |
2016年 | 45篇 |
2015年 | 75篇 |
2014年 | 167篇 |
2013年 | 187篇 |
2012年 | 104篇 |
2011年 | 188篇 |
2010年 | 167篇 |
2009年 | 153篇 |
2008年 | 148篇 |
2007年 | 161篇 |
2006年 | 141篇 |
2005年 | 99篇 |
2004年 | 128篇 |
2003年 | 92篇 |
2002年 | 57篇 |
2001年 | 39篇 |
2000年 | 43篇 |
1999年 | 38篇 |
1998年 | 31篇 |
1997年 | 33篇 |
1996年 | 31篇 |
1995年 | 38篇 |
1994年 | 46篇 |
1993年 | 37篇 |
1992年 | 40篇 |
1991年 | 33篇 |
1990年 | 41篇 |
1989年 | 31篇 |
1988年 | 37篇 |
1987年 | 42篇 |
1986年 | 36篇 |
1985年 | 30篇 |
1984年 | 36篇 |
1983年 | 21篇 |
1982年 | 21篇 |
1981年 | 27篇 |
1980年 | 20篇 |
1979年 | 13篇 |
1978年 | 9篇 |
1977年 | 13篇 |
1976年 | 10篇 |
1972年 | 7篇 |
1971年 | 10篇 |
排序方式: 共有3054条查询结果,搜索用时 15 毫秒
81.
82.
水稻幼穗组培及白化苗的电镜观察 总被引:7,自引:0,他引:7
木文报道了五份水稻材料的幼穗组培的诱导率和分化率,对继代8次后的幼穗愈伤分化出的白苗和绿苗及其各自的愈伤进行电镜扫描,发现白苗的质体结构不完整,不能正常合成叶绿素。 相似文献
83.
荷兰菊组织培养快繁技术研究 总被引:3,自引:0,他引:3
本文利用组织培养技术研究荷兰菊的快速繁殖,为大量培育荷兰菊种苗提供可靠方法。通过多种培养基的试验筛选,找出较满意的培养方法、三种培养基依次使用,可以达到快速繁殖目的。三种培养基分别是:MS+KTO·lmg/l+糖209/1+琼脂7g/l、MS+6—BA5mg/l+NAAO.01mg/l+糖209/l+琼脂7g/l、1/ZMS+NAAO.lmg/l+糖20g/l+琼脂7g/l·三种培养基pH均为6。 相似文献
84.
B. Arnholdt-Schmitt S. Herterich K. -H. Neumann 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1995,91(5):809-815
Investigations were performed on growth phase-dependent EcoRII site-specific DNA methylation of the carrot genome during primary culture to elucidate physiological aspects of genome DNA variability in tissue culture. While DNA methylation of the root cambium and the secondary phloem and petioles of carrot leaves were strikingly different, the methylation level of the secondary phloem seemed to be independent of cultivar origin, the age of the plants and the extent of secondary root growth. As was shown earlier a change in the differentiated state of the secondary phloem by tissue culture leads to changes in genome modification. Whereas de novo methylation was observed during the first 2 weeks of growth initiation, the results presented demonstrate genome de-methylation during the transition to stationary growth indicating differential nome methylation during different phases of culture. The presence of kinetin in the nutrient medium of the primary culture was found to be antagonistic to changes in genome modification in general. De novo methylation and subsequent de-methylation of the carrot genome are discussed as gross changes obviously essential to molecular genome differentiation during tissue culture. 相似文献
85.
† Michel Bureau †Jacques Laschet Mercédès Bureau-Heeren Benoît Hennuy Arlette Minet Pierre Wins Thierry Grisar 《Journal of neurochemistry》1995,65(5):2006-2015
Abstract: GABAA receptors were characterized in cellular fractions isolated from adult bovine brain. The fraction enriched in cortical astrocytes is very rich in high-affinity binding sites for [3 H]flunitrazepam and other "central-type" benzodiazepine ligands. The amount of specific [3 H]flunitrazepam binding was more than five times higher in the glial fraction than in synaptosomal and perikaryal fractions. [3 H]Flunitrazepam was displaced by low concentrations of clonazepam and other specific ligands for central GABAA receptors. Specific binding sites for GABA, flunitrazepam, barbiturates, and picrotoxin-like convulsants were characterized. Allosteric interactions between the different sites were typical of central-type GABAA receptors. The presence of α-subunit(s), as revealed by [3 H]flunitrazepam photoaffinity labeling, was demonstrated in all brain fractions at molecular mass 51–53 kDa. Photoaffinity labeling was highest in the glial fraction. However, in primary cultured astrocytes from neonate rat cortex, no photoaffinity labeling was detected. Information obtained from astrocytes in culture should thus be taken with caution when extrapolated to differentiated astroglial cells. Our results actually show that, in mature brain, most of the fully pharmacologically active GABAA receptors are extrasynaptic and expressed in astroglia. 相似文献
86.
MDCK cell monolayers grown on glass coverslips were used to examine the Na+ concentration in individual lateral intercellular spaces (LIS) by video fluorescence microscopy. The LIS was filled with the Na+-sensitive fluorescent dye SBFO by incubation of the monolayers for 75–90 min with 250 m of the membrane impermeant form of the dye. After dye loading, the monolayers were perfused at 37°C with solutions buffered with HEPES or bicarbonate/CO2 containing 142 mm Na+. Ratios of the fluorescence images after sequential excitation with 340 nm and 380 nm light were performed and in situ calibration of LIS Na+ was accomplished after blocking the Na+ pump with 5 × 10–4 m ouabain. Measurements of Na+ along the basolateral-to-apical axis of the LIS at 1.0 or 1.5 m intervals did not reveal a Na+ gradient when the perfusate was either HEPES or bicarbonate/CO2 solutions. In bicarbonate solutions, the mean Na+ concentration (mm) was 157.2 ± 2.3, 15 mm higher than the bath Na+ concentration. In HEPES solutions, however, the Na+ concentration was not different from the bath concentration (142.7 ± 3.1 mm). The time course of Na+ changes in LIS was investigated by rapidly switching the perfusate from 142 to 80 mm Na+ and measuring the Na+ changes at one focal plane.We would like to thank P.H. Tran and C. Gibson for their technical and computational assistance as well as Dr. B.-E. Persson (University of Uppsala, Sweden) for his contribution in the early phases of the study. 相似文献
87.
Bernard N. Violand Michael R. Schlittler Kevin L. Duffin Christine E. Smith 《Journal of Protein Chemistry》1995,14(5):341-347
The disulfide bond assignments of human alanyl tissue factor pathway inhibitor purified fromEscherichia coli have been determined. This inhibitor of the extrinsic blood coagulation pathway possesses three Kunitz-type inhibitor domains, each containing three disulfide bonds. The disulfide bond pairings in domains 1 and 3 were determined by amino acid sequencing and mass spectrometry of peptides derived from a thermolysin digest. However, thermolysin digestion did not cleave any peptide bonds within domain 2. The disulfide bond pairings in domain 2 were determined by isolating it from the thermolysin treatment and subsequently cleaving it with pepsin and trypsin into peptides which yielded the three disulfide bond pairings in this domain. These results demonstrate that the disulfide pairings in each of the three domains of human tissue factor pathway inhibitor purified fromEscherichia coli are homologous to each other and also to those in bovine pancreatic trypsin inhibitor. 相似文献
88.
89.
Stamatina E. Ziemba Shani Saks Yvonne Janviriya Robert S. Stephenson 《Cell and tissue research》1995,280(2):473-477
Photoreceptor cells that were mostly free of extracellular material and suitable for most electrophysiological study procedures were dissociated from whole heads of the fruit fly, Drosophila melanogaster, by a simple smash technique employing gentle chopping by a razor blade through Parafilm sheets. A variety of commonly available proteolytic and glycolytic digestion enzymes were tested as additions to the basic dissociation procedure described. With the aid of Nomarski interference contrast optics, periodic acid-Schiff staining, and fluorescent labeling and microscopy methods, it was determined that proteolytic enzymatic digestion does little to enhance the dissociation procedure, and instead, often damages the cells that one is attempting to recover. Unexpectedly, certain glycolytic enzymes, when added to the basic procedure, appear to enhance the recovery of intact viable Drosophila photoreceptors that are stripped of most extracellular material. Based on these results, a hypothesis concerning the biochemical nature of the extracellular matrix of the Drosophila retina is proposed. Drosophila photoreceptors are an interesting model system for the study of invertebrate phototransduction and photoreceptor cell biology because of their many well-characterized mutant strains. The technique described here should produce clean viable photoreceptors or ommatidia that respond to light, and that are suitable for patch clamping or cell culture. 相似文献
90.
Izaura Yoshico Hirata Maria Helena Sedenho Cezari Clovis Ryuichi Nakaie Paulo Boschcov Amando Siuiti Ito Maria Aparecida Juliano Luiz Juliano 《Letters in Peptide Science》1995,1(6):299-308
Summary A general procedure, using the commonly employed solid-phase peptide synthesis methodology for obtaining internally quenched fluorogenic peptides with ortho-aminobenzoyl/dinitrophenyl groups as donor-acceptor pairs, is presented. The essential feature of this procedure is the synthesis of an N
-Boc or-Fmoc derivative of glutamic acid with the -carboxyl group bound to N-(2,4-dinitrophenyl)-ethylenediamine (EDDnp), which provides the quencher moiety attached to the C-terminus of the substrate. The fluorescent donor group, ortho-aminobenzoic acid (Abz), is incorporated into the resin-bound peptide in the last coupling cycle. Depending on the resin type used, Abz-peptidyl-Gln-EDDnp or Abz-peptidyl-Glu-EDDnp is obtained. Using the procedure described above, substrates for human renin and tissue kallikreins were synthesised. Spectrofluorimetric measurements of Abz bound to the -amino group of proline showed that strong quenching of Abz fluorescence occurs in the absence of any acceptor group. 相似文献