全文获取类型
收费全文 | 6159篇 |
免费 | 548篇 |
国内免费 | 334篇 |
出版年
2024年 | 18篇 |
2023年 | 207篇 |
2022年 | 295篇 |
2021年 | 329篇 |
2020年 | 298篇 |
2019年 | 359篇 |
2018年 | 338篇 |
2017年 | 278篇 |
2016年 | 224篇 |
2015年 | 238篇 |
2014年 | 363篇 |
2013年 | 398篇 |
2012年 | 255篇 |
2011年 | 359篇 |
2010年 | 240篇 |
2009年 | 259篇 |
2008年 | 287篇 |
2007年 | 269篇 |
2006年 | 245篇 |
2005年 | 223篇 |
2004年 | 201篇 |
2003年 | 189篇 |
2002年 | 135篇 |
2001年 | 78篇 |
2000年 | 91篇 |
1999年 | 70篇 |
1998年 | 54篇 |
1997年 | 55篇 |
1996年 | 37篇 |
1995年 | 34篇 |
1994年 | 35篇 |
1993年 | 29篇 |
1992年 | 19篇 |
1991年 | 19篇 |
1989年 | 13篇 |
1988年 | 12篇 |
1987年 | 26篇 |
1986年 | 17篇 |
1985年 | 35篇 |
1984年 | 53篇 |
1983年 | 49篇 |
1982年 | 45篇 |
1981年 | 46篇 |
1980年 | 32篇 |
1979年 | 36篇 |
1978年 | 43篇 |
1977年 | 27篇 |
1976年 | 14篇 |
1975年 | 18篇 |
1974年 | 22篇 |
排序方式: 共有7041条查询结果,搜索用时 15 毫秒
31.
Theodore G. Gabig Bruce A. Lefker 《Biochemical and biophysical research communications》1984,118(2):430-436
The resolved flavoprotein and cytochrome b559 components of the NADPH dependent generating oxidase from human neutrophils were the subject of further study. The resolved flavoprotein, depleted of cytochrome b559, was reduced by NADPH under anaerobic conditions and reoxidized by oxygen. NADPH dependent generation by the resolved flavoprotein fraction was not detectable, however it was competent in the transfer of electrons from NADPH to artificial electron acceptors. The resolved cytochrome b559, depleted of flavoprotein, demonstrated no measureable NADPH dependent generating activity and was not reduced by NADPH under anaerobic conditions. The dithionite reduced form of the resolved cytochrome b559 was rapidly oxidized by oxygen, as was the cytochrome b559 in the intact oxidase. 相似文献
32.
Gideon Bach Elizabeth F. Neufeld 《Biochemical and biophysical research communications》1983,112(1):198-205
The biosynthesis of arylsulfatase A was studied in cultured fibroblasts by pulse-chase labeling with [2-3H]mannose; the enzyme was isolated by immunoprecipitation and denaturing polyacrylamide gel electrophoresis. In normal fibroblasts, and in fibroblasts from a patient with multiple sulfatase deficiency, the enzyme was synthesized as a glycoprotein of apparent molecular weight of 59,000; half of it was processed over a period of 4 days to Mr= 57,000. The precursor chain of Mr= 59,000 was secreted in the presence of 10 mM NH4Cl. An immunoprecipitable glycoprotein of normal size was synthesized by fibroblasts from two unrelated patients with metachromatic leukodystrophy, but this material disappeared within twenty hours. In fibroblasts from an individual with pseudodeficiency of arylsulfatase A, the immunoprecipitable precursor glycoprotein was smaller (Mr= 56,000). The synthesis of cross-reactive proteins with altered properties supports the concept of allelic mutations as the genetic basis of metachromatic leukodystrophy and of arylsulfatase A pseudodeficiency. 相似文献
33.
DANIELLE ROJAS-ROUSSE DJALAL ESLAMI PAULETTE LAGRANGE 《Entomologia Experimentalis et Applicata》1983,34(3):317-325
Lorsque 2 femelles ou 3 femelles de l'ectoparasite D. vagabundus parasitent conjointement un même lot d'hôtes l'intensité du grégarisme larvaire s'accroît par rapport à celui observé en présence d'une seule femelle pondeuse. Cela se traduit par une augmentation significative du nombre moyen de descendants des 2 sexes mais la production moyenne en fils est toujours très inférieure à celle des filles. Cependant, lorsque la densité de femelles pondeuses passe de 1 à 3, le rapport des sexes mâles/femelles des descendants évolue vers l'unité traduisant une augmentation plus rapide de l'effectif des fils que des filles. 相似文献
34.
Comparison of six rabbit liver cytochrome P-450 isozymes in formation of a reactive metabolite of acetaminophen 总被引:7,自引:0,他引:7
This laboratory has recently reported the isolation of an ethanol-inducible form of rabbit liver microsomal cytochrome P-450, designated isozyme 3a. In view of the reports of others that the hepatotoxicity of acetaminophen is increased in ethanol-treated animals and the human alcoholic, we have determined the activity of the six available P-450 isozymes in the activation of the drug to give an intermediate which forms a conjugate with reduced glutathione. Isozymes 3a, 4, and 6, all of which are present in significant amounts in the liver microsomes from rabbits chronically administered ethanol, exhibited the highest activities in the reconstituted enzyme system, whereas isozymes 3b and 3c were 10- to 20-fold less effective, and phenobarbital-inducible isozyme 2 was essentially inactive, even in the presence of cytochrome b5. The results obtained thus indicate that induction by ethanol of P-450 isozyme 3a (or a homologous enzyme in other species) may contribute to the toxicity of acetaminophen but that other cytochromes also play a significant role. 相似文献
35.
The association between bleomycin-induced chromatid aberrations and BUdR-label exchange between sister chromatids was investigated in order to evaluate Revell's exchange hypothesis for the formation of chromatid aberrations. The results of this study indicate that a larger than expected proportion of chromatid breaks can be accounted for by the exchange hypothesis though not all breaks are the result of incomplete exchange. 相似文献
36.
A hitherto unknown hydroxy acid has been isolated from Blepharis sindica seed oil has been characterized as 9-hydroxydodecanoic acid by IR, NMR and mass spectral studies. The structure of this acid was further supported by its chemical transformations. 相似文献
37.
The accumulation of transported materials in cut axons is demonstrated by the light and electron microscopic immunocytochemical localization of substance P and enkephalin in the caudal medulla and cervical spinal cord of adult rat. Two days following unilateral knife-cuts in the caudal medulla or spinal (C2-C3) levels, substance P and enkephalin-like immunoreactivity (SPLI and ELI) are detected in lesioned axons located rostral and caudal to the transection. Rostrally, SPLI and ELI are detected in the lateral reticular region and ventrolateral fasciculus corresponding to the location of previously identified bulbospinal pathways. Caudally, previously unidentified, propriospinal pathways showing SPLI are detected in the dorsal columns and in the dorsolateral fasciculus. In contrast, ELI is found caudal to the transection only in the reticular region of the medulla. For both peptides, immunoreactivity is present throughout axons containing numerous large, dense core, and small clear vesicles. These results support the concept of both particulate and soluble modes of transport for substance P and enkephalin within axons of the central nervous system. 相似文献
38.
Suppression of natural killer activity in human blood and bone marrow cultures by bone marrow-adherent OKM1-positive cells 总被引:2,自引:0,他引:2
Maintenance and regulation of natural killer (NK) cell activity in human bone marrow cultures were studied using K562 leukemia cells as targets. Culture of bone marrow cells in medium supporting long-term generation of myeloid cells resulted in a rapid loss of NK activity in 1-3 days. In contrast, antibody-dependent cytotoxicity to an NK-resistant tumor was maintained for more than 7 weeks. Horse serum, a component of the myelopoietic culture medium, was found to diminish NK cytotoxicity of blood and bone marrow cultures whereas hydrocortisone supplement did not. In addition, an adherent cell is present in bone marrow which greatly inhibits NK activity. Nonadherent bone marrow cells exhibited higher cytotoxicity than unfractionated cells at all days of culture; adherent cells were not cytotoxic to K562. Purified adherent marrow cells inhibited the cytotoxic capacity of nonadherent blood or marrow mononuclear cells during coculture. Indomethacin, an inhibitor of protaglandin synthesis, augmented levels of NK activity in cultures of bone marrow cells, indicating that macrophages may be suppressing this effector function via prostaglandins. Further identification of the adherent suppressor cells came from experiments in which suppression was prevented by treatment of the adherent cells with monoclonal OKM1 antibody plus complement. This study shows that bone marrow-adherent OKM1-positive cells, presumably macrophages, negatively regulate NK activity, and it defines conditions for analysis of the generation and/or positive regulation of NK cells in human bone marrow. 相似文献
39.
C. A. Schreiner D. A. Edwards R. H. McKee M. Swanson Z. A. Wong S. Schmitt P. Beatty 《Cell biology and toxicology》1989,5(2):169-188
Catalytic reforming is a refining process that converts naphthenes to aromatics by dehydrogenation to make higher octane gasoline blending components. A portion of this wide boiling range hydrocarbon stream can be separated by distillation and used for other purposes. One such application is a mixture of predominantly 9-carbon aromatic molecules (C9 aromatics, primarily isomers of ethyltoluene and trimethylbenzene), which is removed and used as a solvent — high-flash aromatic naphtha. A program was initiated to assess the toxicological properties of high-flash aromatic naphtha since there may be human exposure through inhalation or external body contact. The current study was conducted partly to assess the potential for mutagenic activity and also to assist in an assessment of carcinogenic potential. The specific tests utilized included the Salmonella/mammalian microsome mutagenicity assay, the hypoxanthine-guanine phosphoribosyl transferase (HGPRT) forward mutation assay in CHO cells, in vitro chromosome aberration and sister chromatid exchange (SCE) assays in CHO cells, and an in vivo chromosome aberration assay in rat bone marrow.There was no evidence that high-flash aromatic naphtha was either a gene or chromosomal mutagen. Thus it is unlikely to be a genotoxic carcinogen.Abbreviations Brdu
5-Bromo-2-deoxyuridine
- C9
Aromatic species with 9 carbons (i.e., ethyl toluene and trimethyl benzene isomers)
- CE
Cloning efficiency
- CHO
Chinese hamster embryo
- CP
Cyclophosphamide
- DMSO
Dimethyl sulfoxide
- HGPRT
Hypoxanthine-guanine phosphoribosyl transferase
- HVAC
Heating, Ventilation, Air Conditioning
- 3MC
3 Methylcholanthrene
- MMC
Mitomycin C
- MMS
Methyl methanesulfonate
- S9
S9 Mammalian microsomal enzyme activation mixture
- SCE
Sister chromatid exchange 相似文献
40.
Tadao Hashimoto Yukuo Yoshida Kunio Tagawa 《Journal of bioenergetics and biomembranes》1990,22(1):27-38
An intrinsic ATPase inhibitor inhibits the ATP-hydrolyzing activity of mitochondrial F1F0-ATPase and is released from its binding site on the enzyme upon energization of mitochondrial membranes to allow phosphorylation of ADP. The mitochondrial activity to synthesize ATP is not influenced by the absence of the inhibitor protein. The enzyme activity to hydrolyze ATP is induced by dissipation of the membrane potential in the absence of the inhibitor. Thus, the inhibitor is not responsible for oxidative phosphorylation, but acts only to inhibit ATP hydrolysis by F1F0-ATPase upon deenergization of mitochondrial membranes. The inhibitor protein forms a regulatory complex with two stabilizing factors, 9K and 15K proteins, which facilitate the binding of the inhibitor to F1F0-ATPase and stabilize the resultant inactivated enzyme. The 9K protein, having a sequence very similar to the inhibitor, binds directly to F1 in a manner similar to the inhibitor. The 15K protein binds to the F0 part and holds the inhibitor and the 9K protein on F1F0-ATPase even when one of them is detached from the F1 part. 相似文献