全文获取类型
收费全文 | 3163篇 |
免费 | 163篇 |
国内免费 | 75篇 |
出版年
2023年 | 21篇 |
2022年 | 30篇 |
2021年 | 50篇 |
2020年 | 64篇 |
2019年 | 74篇 |
2018年 | 53篇 |
2017年 | 75篇 |
2016年 | 51篇 |
2015年 | 84篇 |
2014年 | 173篇 |
2013年 | 199篇 |
2012年 | 125篇 |
2011年 | 189篇 |
2010年 | 168篇 |
2009年 | 150篇 |
2008年 | 150篇 |
2007年 | 172篇 |
2006年 | 147篇 |
2005年 | 109篇 |
2004年 | 132篇 |
2003年 | 100篇 |
2002年 | 63篇 |
2001年 | 38篇 |
2000年 | 51篇 |
1999年 | 50篇 |
1998年 | 37篇 |
1997年 | 41篇 |
1996年 | 41篇 |
1995年 | 51篇 |
1994年 | 65篇 |
1993年 | 55篇 |
1992年 | 52篇 |
1991年 | 46篇 |
1990年 | 48篇 |
1989年 | 38篇 |
1988年 | 45篇 |
1987年 | 41篇 |
1986年 | 41篇 |
1985年 | 41篇 |
1984年 | 44篇 |
1983年 | 26篇 |
1982年 | 27篇 |
1981年 | 33篇 |
1980年 | 27篇 |
1979年 | 13篇 |
1978年 | 12篇 |
1977年 | 13篇 |
1976年 | 12篇 |
1973年 | 7篇 |
1971年 | 10篇 |
排序方式: 共有3401条查询结果,搜索用时 31 毫秒
101.
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
102.
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
103.
G.W. Meijer J.E.M. Groener A.C. Beynen A. Van Tol 《Comparative biochemistry and physiology. Part B, Biochemistry & molecular biology》1996,114(4):403-407
We investigated the relationship between the development of hypercholesterolemia in rabbits and cholesteryl ester transfer protein (CETP) activity secretion by their perfused livers. Two inbred strains of rabbits were compared which differ markedly in their hypercholesterolemic response to dietary cholesterol. Feeding a high-cholesterol (0.3%) diet, increased plasma and liver cholesterol levels in the two strains, the increments being 15 mM and 30 μmol/g greater in the hyperresponders, respectively. The high-cholesterol diet caused an about 2-fold increased hepatic secretion of CETP activity, but there was no difference between the two rabbit strains. Feeding a lower amount of dietary cholesterol (0.08%) also caused higher cholesterolemic (2 mM) and hepatocholesterolic (28 μmol/g) responses in hyper- than in hyporesponsive rabbits. The activity of hepatic CETP secretion was not increased by the low-cholesterol diet, and there was no difference between hypo- and hyperresponsive rabbits. Cholesterol feeding increased plasma CETP activity by 90% in both rabbit strains, but there was no difference between the strains. Our combined data suggest that with increasing plasma cholesterol levels, hepatic CETP secretion may be increased in a parabolic manner, reaching its maximum rate far before plasma cholesterol concentrations are maximal. There were no differences in hepatic CETP activity secretion or plasma CETP activity levels between the genetically different strains of hypo- and hyperresponsive rabbits. 相似文献
104.
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
105.
† 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
106.
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
107.
Omasa T Kobayashi M Nishikawa T Shioya S Suga K Uemura S Kitani Y Imamura Y 《Biotechnology and bioengineering》1995,48(6):673-680
The effects of the high-molecular-weight growth factors, transferrin and bovine serum albumin (BSA), on antibody production were analyzed quantitatively in continuous hollow-fiber cultivation over a period of 60 days. Transferrin enhanced cell growth but had no significant effect on the specific antibody production rate, whereas BSA significantly enhanced antibody production. The antibody production rate was increased 4- and 14-fold respectively by feeding BSA at 2 and 5 g L(-1) into the EC side of the system (the side connected to the cell-containing outer part of the hollow-fiber unit) compared with the production achieved without BSA. Addition of 5 g L(1) BSA into the IC side of the system (the side connected to the inner part of the hollow-fiber unit) resulted in a 2.5-fold increase in the antibody production rate. The effect of BSA was also analyzed using the perfusion culture system with a separation unit. When fresh medium containing either 2 or 5 g L(-1) BSA was fed into the reactor, both the specific growth rate and specific death rate increased, while the specific antibody production rate was increased 2- and 25-fold, respectively, by feeding BSA at these two concentrations compared with no addition. Comparing the two systems, the increase in the antibody production rate achieved with the hollow-fiber system was threefold greater than that in the perfusion culture system with the same concentration of BSA feeding. (c) 1995 John Wiley & Sons, Inc. 相似文献
108.
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
109.
Evaluation of the serum-free medium MDSS2 for the production of poliovirus on vero cells in bioreactors 总被引:2,自引:0,他引:2
The serum-free medium MDSS2 (Merten et al., 1994), was used for cultivating Vero cells as well as for producing poliovirus
(Sabin type 1) in static and in perfused micro-carrier cultures. At slightly different growth rates of 0.0120/h and 0.0106/h,
respectively, static cultures in serum-containing (SCM) and serum-free (SFM) medium produced titers of 106.75 and 106.67 TCID50 per 50 μl; signifying a specific productivity of 0.89 and 1.07 TCID50/c.
Serum-free bioreactor cultures of Vero cells on DEAE-dextran microcarriers at 6.25 g/l produced cell densities of about 1.5×106c/ml. After infection with virus (multiplicity of infection (MOI) 0.1–0.3) titers of about 6.3×108 TCID50/ml were obtained, signifying an average specific productivity of 7.1 TCID50/c.h. Although these values were 4 and
2 fold, respectively, higher than in classical resum-based production processes (Montagnon et al. Dev. biol. Stand. 1981,
47, 55), a reference culture, for which cell growth was done in SCM and only virus production was done in SFM, produced 2×109 TCID/ml with an average specific virus production rate of 18.9 TCID50/c.h. The differences between the fully serum-free and
our reference process were mainly due to physiological differences of cells grown in SCM and SFM and also due to strongly
modified consumption kinetics after virus infection leading to limitations of one or several essential medium compounds, like
glucose and amino acids. Avoiding these limitations by increasing the residual concentration of glucose, glutamine, histidine,
and SH-amino acids, led to specific virus production rates (of about 17.9 TCID59/c.h.) comparable to those found in the reference
virus production process. The optimisation of the production of the poliovirus (Sabin 1) will be described with respect to
the modification of the medium composition.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
110.
Summary Insitu perfusion of rat liver was performed with a medium containing glucose-cysteine adduct [2-(D-gluco-pentahydroxypentyl) thiazolidine-4-carboxylic acid, glc-cys] and its effect on glutathione (GSH) and ATP levels and bile production was examined. The GSH content in the liver was maintained at the original level during perfusion with 1 mM glc-cys for 2h, while it decreased significantly in the absence of glc-cys. After 4h of perfusion without glc-cys, ATP content and bile production decreased significantly besides the decrease in GSH content, but they were maintained at the original levels with glc-cys. When the perfusion was performed with the liver of rats injected with diethyl maleate (DEM), the GSH level, which was decreased to 6.0% of the control by DEM injection, was restored to 22.6% of the original level by perfusion with 2mM glc-cys for 30 min. Data indicate that glccys is a cysteine prodrug with protective action on the liver. 相似文献