全文获取类型
收费全文 | 3271篇 |
免费 | 361篇 |
国内免费 | 4篇 |
专业分类
3636篇 |
出版年
2022年 | 25篇 |
2021年 | 60篇 |
2020年 | 36篇 |
2019年 | 32篇 |
2018年 | 42篇 |
2017年 | 60篇 |
2016年 | 74篇 |
2015年 | 115篇 |
2014年 | 148篇 |
2013年 | 195篇 |
2012年 | 226篇 |
2011年 | 248篇 |
2010年 | 159篇 |
2009年 | 134篇 |
2008年 | 186篇 |
2007年 | 217篇 |
2006年 | 190篇 |
2005年 | 204篇 |
2004年 | 173篇 |
2003年 | 193篇 |
2002年 | 177篇 |
2001年 | 50篇 |
2000年 | 32篇 |
1999年 | 48篇 |
1998年 | 47篇 |
1997年 | 41篇 |
1996年 | 35篇 |
1995年 | 36篇 |
1994年 | 36篇 |
1993年 | 22篇 |
1992年 | 27篇 |
1991年 | 20篇 |
1990年 | 24篇 |
1989年 | 32篇 |
1988年 | 21篇 |
1987年 | 14篇 |
1986年 | 13篇 |
1985年 | 12篇 |
1984年 | 20篇 |
1982年 | 15篇 |
1981年 | 14篇 |
1980年 | 11篇 |
1979年 | 18篇 |
1978年 | 16篇 |
1976年 | 15篇 |
1974年 | 11篇 |
1973年 | 10篇 |
1972年 | 11篇 |
1970年 | 14篇 |
1969年 | 10篇 |
排序方式: 共有3636条查询结果,搜索用时 15 毫秒
1.
2.
W Tymiński E Czestochowska A Hellmann A Kreglewski 《Folia haematologica (Leipzig, Germany : 1928)》1980,107(2):269-272
Coagulation and fibrinolysis were measured in the portal and peripheral circulation in 15 rabbits after ligation of the superior mesenteric artery. It was found that the local coagulation syndrome in the mesenteric region can be recognized by tests in blood samples taken from the peripheral circulation area. 相似文献
3.
H J Gabius A Bardosi S Gabius K P Hellmann M Karas H Kratzin 《Biochemical and biophysical research communications》1989,163(1):506-512
A Ca2+-dependent sialic acid-binding protein was purified on fetuin-Sepharose from various types of human tissue. The molecular mass was determined to be 10,315 Da by laser desorption mass spectrometry. Partial sequence analysis after cyanogen bromide cleavage that yielded one N-terminus accessible for Edman degradation revealed an identity to an internal stretch following the only methionine residue within a putative amino acid sequence (Mr 10,048), deduced from the cDNA of a cell cycle-specific gene. The reported biochemical identification is a prerequisite to infer the biological role of the so far undetected gene product. Initial glycohistochemical studies with sialic acid-(BSA-biotin) raised evidence for nuclear localization of sialic acid-binding sites that might reflect, at least in part, detection of this protein. 相似文献
4.
Based on cross-sectional and longitudinal data collected in 1967–1988 by various observers, male reproductive success was
studied in the Hanuman langurs of Jodhpur, India. The harem-structured social organization ensures a high degree of paternity
certainty. Births occur throughout the year, with significant peaks and minima in March and November, respectively (n =398).The interbirth interval averages 16.7 months (n = 114).The duration of harem residencies varies between 3 days and ≥ 74.0 months, with a mean of 26.5 (n = 64). Harem holder replacements
occur during all months of the year. No male achieves residency in more than one troop, suggesting that residency is associated
with a distinct peak in the resource holding potential of a given male. Reproductive success among males varies considerably.
Male mortality is high due to migration and intrasexual competition, leading to an adult sex ratio of 1:4.9. It is estimated
that one-quarter of all adult males will never gain harem residency. Conceptions achieved outside harem residencies are so
rare (4.7%) that a viable low-risk strategy, opting for longevity instead of harem residency, is unlikely. Tenure length has
a stronger influence on male reproductive success than harem size because interbirth intervals are significantly shorter in
small harems than in larger ones. It is assumed that females in one-male breeding structures compete for sperm and that such
competition is more intense in larger harems. 相似文献
5.
The activity of beta-adrenergic receptors at the plasma membrane level was investigated in viable, electropermeabilized C6 glioma cells. Electric field pulses were applied directly to the plated cells without any previous proteinase treatment. The affinity for isoproterenol and the density of the beta-adrenergic receptors, as judged from the number of [3H]CGP-12177 binding sites, were not affected by the electropermeabilization whereas the isoproterenol-stimulated cAMP accumulation was transiently impaired. This decrease in activity is due to an electropermeabilization-induced GTP leak. Normal activity could be obtained either by treating the cells by the electric field in a GTP-containing buffer, or by spontaneous recovery of the cells after the resealing of the plasma membrane, with a delay depending on the temperature. The activity of the receptors was not affected by the structural organization of the membrane associated to its electropermeabilization. 相似文献
6.
7.
Armin Bohmann Ralf Pörtner Jörg Schmieding Volker Kasche Herbert Märkl 《Cytotechnology》1992,9(1-3):51-57
A hybridoma cell was cultivated continuously in a membrane dialysis bioreactor with an integrated radial-flow fixed bed consisting of porous Siran® carriers over a period of 6 weeks. Antibodies accumulated to an average of 100 mg l?1, approx. 10 times more than in fixed bed cultures without dialysis membrane. Serum costs could be reduced about 85% due to an appropriate feeding strategy. Siran® carriers with 3–5 mm diameter showed an advantage compared to those with 1–2 mm diameter. For the 3–5 mm carrier the specific glucose uptake rate and the MAb production rate were constant, if the velocity was between 0.09 mm s?1 and 0.75 mm s?1. At higher velocities cells are washed out of the bed. Furthermore antibody consistency and cell stability were verified in long-term cultivations over a period of 96 days. From an estimation of the antibody concentration reachable with the reactor concept under optimal conditions a concentration 45 times higher compared to axial-flow fixed bed reactors and 11 times higher compared to stirred tank reactors can be expected. 相似文献
8.
Summary In bacteria 5-aminolevulinate, the universal precursor in the biosynthesis of the porphyrin nucleus of hemes, chlorophylls and bilins is synthesised by two different pathways: in non-sulphur purple bacteria (Rhodobacter) or Rhizobium 5-aminolevulinate synthase condenses glycine and succinyl-CoA into 5-aminolevulinate as is the case in mammalian cells and yeast. In cyanobacteria, green and purple sulphur bacteria, as in chloroplasts of higher plants and algae a three step pathway converts glutamate into 5-aminolevulinate. The last step is the conversion of glutamate 1-semialdehyde into 5-aminolevulinate. Using a cDNA clone encoding glutamate 1-semialdehyde aminotransferase from barley, genes for this enzyme were cloned from Synechococcus PCC6301 and Escherichia coli and sequenced. The popC gene of E. coli, previously considered to encode 5-aminolevulinate synthase, appears to be a structural gene for glutamate 1-semialdehyde aminotransferase. Domains with identical amino acid sequences comprise 48% of the primary structure of the barley, cyanobacterial and putative E. coli glutamate 1-semialdehyde aminotransferases. The cyanobacterial and barley enzymes share 72% identical residues. The peptide containing a likely pyridoxamine phosphate binding lysine is conserved in all three protein sequences. 相似文献
9.
Volker Nicolai 《Oecologia》1991,88(1):132-137
Summary The arthropod communities living on the bark of the oak species Quercus macrocarpa and Q. ellipsoidalis were investigated in a North American oak savanna. Differences were found in the community structure of the arthropods living on the bark of these two tree species, although they have the same fissured bark type. In the North American oak savanna ecosystem the most important disturbance factor is fire, which maintains species richness. Highest numbers of species and specimens were found at moderately disturbed sites. Three main ecological groups of arthropods living on the bark of trees can be distinguished in relation to the degree of disturbance: (1) Inhabitants of bark of trees restricted to undisturbed sites: they do not occur in fire-disturbed areas; (2) Inhabitants of bark of trees adapted to a moderate degree of disturbance: many species occur in high numbers only in moderately disturbed areas; and (3) Specialist inhabitants of bark of trees in heavily disturbed areas. The number of specimens of these species increases per trunk with the frequency of disturbance. 相似文献
10.
Volker Schirrmacher Paul von Hoegen Andreas Griesbach Hans-Jörg Schild Uwe Zangemeister-Wittke 《Cancer immunology, immunotherapy : CII》1991,32(6):373-381
Summary DBA/2 (H-2d) mice bearing a transplanted highly metastatic lymphoma (ESb) in a state of widely disseminated disease could be successfully treated by a combination of surgery (removal of the local tumour), irradiation (5 Gy) and adoptive immunotherapy. The immunotherapy was achieved by transfer of anti-ESb-immune spleen cells from B10.D2 mice, which express the same major histocompatibility complex (MHC) molecules as DBA/2. In contrast, anti-ESb-immune cells from MHC-disparate C57BL/6 mice did not confer protective immunity. The B10.D2 anti-ESb-immune T cells contain two types of cytolytic specificity as detected by limiting-dilution analysis: (1) clones with specificity for the ESb-tumour-associated transplantation antigen (TATA) (at low frequency), and (b) clones with specificity for minor DBA/2 histocompatibility (H) antigens (at high frequency). Immune B10.D2 cells raised against different tumour lines or against TATA– ESb tumour variants did not confer the 100% protection seen with immune cells against ESb TATA+ cells. Finally we demonstrate that the allogeneic immune cells are more potent in terms of protective immunity than corresponding syngeneic immune cells. The data suggest that the strong graft-versus-leukemia effect with immune T cells from allogeneic MHC-identical but not from MHC-disparate mice was due to T cells with MHC-restricted specificity for an ESb-associated TATA. A graft-versus-host reactivity that developed much later and could not be prevented was most likely due to T cells sensitized against normal minor H antigens of the host. Our results are of potential relevance for allogeneic bone marrow transplantation and adoptive immunotherapy protocols. 相似文献