全文获取类型
收费全文 | 12299篇 |
免费 | 1196篇 |
国内免费 | 1436篇 |
出版年
2024年 | 24篇 |
2023年 | 452篇 |
2022年 | 452篇 |
2021年 | 623篇 |
2020年 | 610篇 |
2019年 | 647篇 |
2018年 | 533篇 |
2017年 | 490篇 |
2016年 | 447篇 |
2015年 | 500篇 |
2014年 | 544篇 |
2013年 | 853篇 |
2012年 | 432篇 |
2011年 | 523篇 |
2010年 | 430篇 |
2009年 | 524篇 |
2008年 | 583篇 |
2007年 | 631篇 |
2006年 | 540篇 |
2005年 | 496篇 |
2004年 | 429篇 |
2003年 | 445篇 |
2002年 | 425篇 |
2001年 | 348篇 |
2000年 | 258篇 |
1999年 | 293篇 |
1998年 | 246篇 |
1997年 | 239篇 |
1996年 | 220篇 |
1995年 | 177篇 |
1994年 | 188篇 |
1993年 | 136篇 |
1992年 | 149篇 |
1991年 | 133篇 |
1990年 | 88篇 |
1989年 | 89篇 |
1988年 | 66篇 |
1987年 | 58篇 |
1986年 | 50篇 |
1985年 | 97篇 |
1984年 | 98篇 |
1983年 | 67篇 |
1982年 | 73篇 |
1981年 | 49篇 |
1980年 | 42篇 |
1979年 | 34篇 |
1978年 | 24篇 |
1977年 | 21篇 |
1976年 | 18篇 |
1973年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
The life stages ofEntomophaga grylli (Fresenius) Batko Pathotype 2 were purified and separated by centrifugation in PercollR density-gradient medium. The ranges of buoyant densities for germinated resting spores, germ conidia, and resting spores
respectively were: 1.040–1.050, 1.055–1.085, and 1.080–1.120 g/ml. Cuticular invasion by germinated germ conidia was the means
by whichMelanoplus grasshoppers became infected. Scanning electron micrographs revealed germination of germ conidia on the visible host integument
at 100% RH, but not at 90% RH. Significantly higher mortality (P<0.05) was obtained after 3 weeks with grasshoppers incubated
in constant light than in constant dark for 24 h following treatment. The disease was not transmitted by ingestion of any
life stage.
Contribution No 85-153-J, Department of Entomology. Agricultural Experiment Station, Kansas State University, Manhattan, KS 66506. 相似文献
102.
A direct radioimmunoassay for measuring urinary 20-hydroxyprogesterone cross-reactivity to monitor and assess luteal function and detect pregnancy in the lion-tailed macaque (Macaca silenus) is described. Urine samples were collected daily during ten nonconceptive and five conceptive ovarian cycles of five dult female lion-tailed macaques. Urine was analyzed for concentrations of 20α-hydroxypro-gesterone cross-reactivity, estrone conjugates, and creatinine. The strength of the luteal phase in normal nonconceptive cycles (n = 8) is characterized by a maximum sevenfold increase (day 9) in mean 20α-hydroxyprogesterone cross-reactivity over follicular phase levels; the duration, by a 13-day sustained elevation of mean 20α-hydroxyprogesterone cross-reactivity levels. Pregnancy is detectable from 20α-hydroxyprogesterone cross-reactivity values approximately 20 days after the periovulatory estrone conjugate peak (n = 4). Apparent anovulation (n = 1), extended follicular phase (n = 1), and early abortion (n = 1) also are detectable using 20α-hydroxyprogesterone cross-reactivity measurements. 相似文献
103.
104.
C. Michael Bowman Elaine M. Berger Elaine N. Butler Karen M. Toth John E. Repine 《In vitro cellular & developmental biology. Plant》1985,21(3):140-142
Summary Zwitterion buffers are often used to modulate the pH of cell culture medium but their effect on cultured cells is controversial.
We found that addition of 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES) caused superoxide dismutase (SOD) inhibitable
increases in nitroblue tetrazolium dye reduction and SOD and catalase inhibitable decreases in the growth of cultured bovine
pulmonary artery endothelial cells. The findings suggest that HEPES stimulates endothelial cells to make toxic oxygen metabolites
that contribute to decreased cell growth.
This work was supported in part by the National Institutes of Health, Colorado and American Lung Associations, Colorado and
American Heart Associations, the Council for Tobacco Research, and the Kroc, Hill, Swan and Kleberg Foundations. Dr. Bowman
is a Clinician Scientist Awardee of the American Heart Association. 相似文献
105.
Peptidases, highly specific toward several synthetic chromogenic peptides, were found in the mycelia of four arthropod pathogenic fungi: Aphanomyces astaci, Beauveria bassiana, Metarrhizium anisopliae, and Paecilomyces farinosus. A. astaci peptidases had high hydrolyzing activities toward most of the peptides, especially those with arginine in the P1 position, while those of B. bassiana and P. farinosus readily hydrolyzed peptides with valine and arginine, as well as proline and tyrosine in the P2 and P1 positions, respectively. The hydrolyzing capacities of M. anisopliae peptidases were similar to A. astaci, but showed lower specific activities. Casein or azocoll was only hydrolyzed by A. astaci peptidases. B. bassiana and M. anisopliae had a very low hydrolyzing capacity toward casein and could not degrade azocoll. P. farinosus had no hydrolyzing activity toward casein or azocoll. Only peptidases from the crayfish pathogen A. astaci could degrade the crayfish cuticle. The peptidase preparations of A. astaci and B. bassiana hydrolyzing MeO-Suc-Arg-Pro-Tyr-pNA or Bz-Phe-Val-Arg-pNA were of the serine type. The possible importance of peptidase activity of arthropod pathogenic fungi in the infection process is discussed. 相似文献
106.
Amino Acids in Plasma and CSF and Monoamine Metabolites in CSF: Interrelationship in Healthy Subjects 总被引:4,自引:2,他引:2
L. Hagenfeldt L. Bjerkenstedt G. Edman G. Sedvall F.-A. Wiesel 《Journal of neurochemistry》1984,42(3):833-837
Plasma and cerebrospinal fluid (CSF) concentrations of amino acids were measured in 65 healthy volunteers (50 men and 15 women). The CSF levels of the monoamine metabolites homovanillic acid (HVA), 3-methoxy-4-hydroxyphenylethylene glycol (MOPEG), and 5-hydroxyindoleacetic acid (5-HIAA) were also determined. Sex differences were observed in both plasma and CSF amino acid levels as well as in the relationship between these concentrations. No significant correlations were observed between the CSF levels of HVA and 5-HIAA, and the concentrations of their precursor amino acids in either plasma or CSF. The MOPEG level in CSF correlated positively with the plasma concentrations of several amino acids. 相似文献
107.
Structural comparison of the two distinct sugar binding sites in wheat germ agglutinin isolectin II 总被引:12,自引:0,他引:12
C S Wright 《Journal of molecular biology》1984,178(1):91-104
108.
Thomas M. Koval 《In vitro cellular & developmental biology. Plant》1987,23(11):733-737
Summary Insect cell lines are not well-suited to colony formation in liquid medium following low-density cell plating. The present
studies demonstrate that the time of addition of fetal bovine serum to the culture medium and the number of γ-irradiated feeder
cells added to each plate are important factors in developing a useful colony formation assay. TN-368 lepidopteran and WR69-DM-1
dipteran cell lines were used for these experiments. Both cell types display increased plating efficiencies if serum is added
to the medium one or more days prior to plating as compared to adding serum immediately before plating. Growth curves obtained
by seeding cells at higher densities also indicate that cell growth is slightly better if serum is added one or more days
before seeding. These findings are especially important for survival and toxicity studies because the results demonstrate
that even seemingly minor factors involved in cell survival assays may benefit treated cells to a greater degree than untreated
control cells, thus providing an erroneous assessment of cell survival.
This work was supported by USPHS grant R01-CA34158, awarded by the National Cancer Institute, DHHS, Bethesda, MD. 相似文献
109.
In this study, the chromosome constitution of both unfertilized oocytes and fertilized eggs isolated from the oviducts of LT/Sv strain mice were analyzed. Air-dried chromosome preparations from unfertilized oocytes revealed that about one-third of those examined were ovulated as primary oocytes. These were arrested at metaphase of the first meiotic division and exhibited the characteristic “tetrad” chromosome configuration. The remaining two-thirds of the unfertilized oocytes were ovulated at metaphase of the second meiotic division. The fertilized eggs were isolated from the oviducts of LT/Sv females previously mated to (C57BL × CBA) F1 hybrid males. Analysis of the fertilized eggs at metaphase of their first cleavage mitosis revealed that about one-third of the eggs examined were digynic triploids, whereas the remaining two-thirds had the normal diploid chromsome constitution. In the triploids, the 40 female chromosomes present (mouse, n = 20) were derived from a single diploid pronucleus formed after the extrusion of a first polar body, and following the monospermic fertilization of primary oocytes. The female pronuclear-derived chromosomes invariably exhibited “homologous pairing,” and these were associated at their centromeres. The ovulation, penetration, and subsequent fertilization of primary oocytes is an extremely unusual phenomenon in mammals and only appears to occur on a regular basis in LT/Sv mice. The premature “cytoplasmic maturation” of these oocytes is of interest, as they clearly have the same developmental capacity as secondary oocytes. The significance of these observations in relation to folliculogenesis and litter size in LT/Sv mice is discussed. 相似文献
110.
Continuous cell cultures were established from imaginal wing discs of 2 Lepidoptera, Spodoptera frugiperda and Plodia interpunctella. The S. frugiperda line (IAL-SFD1) grows as multicellular vesicles and responds morphologically and biochemically to the insect hormone, 20-hydroxyecdysone. In contrast, the P. interpunctella cells (IAL-PID2) grow as attached monolayers of small spindle-shaped cells and do not appear to have specific responses to 20-hydroxyecdysone, although growth rates are slowed in these cells upon exposure to the hormone. 相似文献