全文获取类型
收费全文 | 10765篇 |
免费 | 801篇 |
专业分类
11566篇 |
出版年
2023年 | 63篇 |
2022年 | 67篇 |
2021年 | 158篇 |
2020年 | 132篇 |
2019年 | 139篇 |
2018年 | 337篇 |
2017年 | 310篇 |
2016年 | 381篇 |
2015年 | 547篇 |
2014年 | 582篇 |
2013年 | 743篇 |
2012年 | 883篇 |
2011年 | 838篇 |
2010年 | 501篇 |
2009年 | 407篇 |
2008年 | 565篇 |
2007年 | 570篇 |
2006年 | 488篇 |
2005年 | 484篇 |
2004年 | 446篇 |
2003年 | 409篇 |
2002年 | 387篇 |
2001年 | 332篇 |
2000年 | 308篇 |
1999年 | 259篇 |
1998年 | 91篇 |
1997年 | 70篇 |
1996年 | 57篇 |
1995年 | 49篇 |
1994年 | 39篇 |
1993年 | 44篇 |
1992年 | 89篇 |
1991年 | 87篇 |
1990年 | 76篇 |
1989年 | 60篇 |
1988年 | 57篇 |
1987年 | 50篇 |
1986年 | 38篇 |
1985年 | 51篇 |
1984年 | 48篇 |
1983年 | 33篇 |
1982年 | 22篇 |
1981年 | 18篇 |
1980年 | 23篇 |
1979年 | 22篇 |
1977年 | 22篇 |
1974年 | 15篇 |
1972年 | 15篇 |
1971年 | 16篇 |
1968年 | 18篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
Eight plant lectins were used to investigate membrane alterations in lymphocytes from patients with chronic lymphocytic leukemia (CLL). By rosetting with lectins attached to latex particles, the cell percentages with the abundance of each lectin receptor were compared in B normal and leukemic lymphocytes. Comparing these data with the number of lectin molecules bound to each cell and the affinity, which are values calculated with 125I-labeled lectins, it was possible to deduce differences in the composition of glycoproteins in B normal and B-CLL lymphocytes membrane. Compared to B normal, B-CLL lymphocytes had fewer receptors for WGA and more for Lens culinaris, SBA and Tetragonolobus purpureus lectins. Receptors for Concanavalin A, Pisum sativum, PHA and Tetragonolobus purpureus showed a higher affinity with B normal lymphocytes, while the other lectins assayed showed more affinity with B-CLL lymphocytes. So, it is possible to establish a comparative analysis about the plasma membrane glycoproteins in the B normal and CLL lymphocytes by lectin binding studies. 相似文献
42.
Manuel J. López-Nieto Filomena R. Ramos José M. Luengo Juan F. Martín 《Applied microbiology and biotechnology》1985,22(5):343-351
Summary The parameters affecting the formation in vivo of -aminoadipyl-cysteinyl-valine (ACV), an intermediate in penicillin biosynthesis, have been established in low- and high-penicillin producing strains ofPenicillium chrysogenum. ACV was found both in cell extracts and in the culture broth filtrates. (14C)valine, -(14C)aminoadipic acid and (14C)cysteine were efficiently incorporated into ACV. Formation of ACV was stimulated by phenylacetic acid when added during the growth of the culture. ACV biosynthesis was enhanced when protein synthesis was blocked with cycloheximide or anisomicin. The ACV-synthesising activity of the culture increased between 24 and 48 h of the culture preceeding penicillin biosynthesis, and remained constant thereafter. A decay of ACV-forming activity was observed when de novo protein synthesis was inhibited with cycloheximide. The apparent half-life of the ACV-synthesising enzyme system was 2.5 h. 相似文献
43.
Norma L. Trolinder Jerry D. Berlin Joe R. Goodin 《In vitro cellular & developmental biology. Plant》1987,23(11):789-794
Summary A cotton cell suspension culture has been developed that provides unique opportunities for plant biologists to investigate
early developmental events regulating cotton fiber properties, plant cell elongation, and cell wall biogenesis. The suspension
culture was derived from cells of cotton (Gossypium hirsutum L.) ovule callus. These cells undergo the stages of fiber development
previously described for in vivo fiber development. Fibers range in length up to 11 mm and have secondary walls.
Supported by the U.S. Department of Agriculture, Agricultural Research Service, Southern Regional Research Laboratory, New
Orleans, Louisiana, and Cotton Incorporated, Raleigh, North Carolina. 相似文献
44.
Carmen Cascales Dan G. Craciunescu Paloma Martín-Sanz María Cascales 《Biological trace element research》1986,11(1):65-73
Enzyme activities and protein content were determined in the cytosolic and mitochondrial fractions of liver homogenates obtained from Rh(III) complex-, thioacetamide- and thioacetamide + Rh(III) complex-treated rats. The Rh(III) complex administered to nonthioacetamide-treated rats produced no significant changes either in the enzymatic activities assayed or in the protein concentration. The Rh(III) complex administered to thioacetamide-treated rats produced significant restoration of the following altered values: cytosolic and mitochondrial aspartate aminotransferase, glutamate dehydrogenase, NADP-isocitrate dehydrogenase, and protein concentration. However, a further increase was produced in the activities of glucose-6-phosphate dehydrogenase and malic enzyme. These increases can be interpreted in terms of an enhancement of the NADPH-dependent detoxifying processes and of nucleic acid synthesis and repair. 相似文献
45.
Summary Two extra bisatellited chromosome identified as inv dup (15) (pterq11.2::q11.2pter) were found in an oligoasthenospermic male. Analysis of Ag-staining in the proband and in one fertile brother with a normal karyotype revealed that nucleolar organizer region (NOR) activity was significantly increased in the patient. The frequency of satellite associations was also significantly higher in the index case, but no correlation was found between NOR activity and acrocentric associations. These results suggest that extra NOR activity and the elevated frequency of satellite associations could predispose to gametogenic impairment. 相似文献
46.
Chromosome pairing in females and males of diploid (2n = 22) and tetraploid (2n = 44) Odontophrynus americanus and diploid Ceratophrys cranwelli (2n = 26) and tetraploid C. ornata (2n = 104) showed that diploid females formed more chiasmata per paired arm than diploid males and polyploids of both sexes. There was a reduction in the level of recombination in female polyploids by forming multivalents with terminal chiasmata. The reduction reflected a change in the genetic control of pairing in females after polyploidization. 相似文献
47.
48.
49.
50.
The photoperiodic variations of testosterone plasmatic levels in male rabbits have been studied. The animals were subjected to the influence of three circadian rhythms: 12/12, 14/10 and 10/14 h of light/darkness. The hormone assay was carried out using an enzymeimmunoassay method (Competitive ELISA). Blood samples were of two different types: seriated and non-seriated, to find if these might be any differences in the results. It is concluded that testosterone plasmatic levels are within physiologic values (0.3-10.0 ng/ml), although differences depending on the light/darkness cycle and on the type of blood extraction are remarkable; for this reason the selection of the circadian rhythm will depend on the experimentation that is to be carried out. 相似文献