全文获取类型
收费全文 | 72778篇 |
免费 | 4922篇 |
国内免费 | 14篇 |
专业分类
77714篇 |
出版年
2023年 | 418篇 |
2022年 | 395篇 |
2021年 | 848篇 |
2020年 | 818篇 |
2019年 | 819篇 |
2018年 | 1923篇 |
2017年 | 1670篇 |
2016年 | 2505篇 |
2015年 | 3476篇 |
2014年 | 3509篇 |
2013年 | 4659篇 |
2012年 | 5840篇 |
2011年 | 5381篇 |
2010年 | 3155篇 |
2009年 | 2439篇 |
2008年 | 4193篇 |
2007年 | 4064篇 |
2006年 | 4008篇 |
2005年 | 3432篇 |
2004年 | 3390篇 |
2003年 | 3111篇 |
2002年 | 2913篇 |
2001年 | 1689篇 |
2000年 | 1738篇 |
1999年 | 1199篇 |
1998年 | 545篇 |
1997年 | 353篇 |
1996年 | 374篇 |
1995年 | 390篇 |
1994年 | 315篇 |
1993年 | 279篇 |
1992年 | 594篇 |
1991年 | 511篇 |
1990年 | 485篇 |
1989年 | 473篇 |
1988年 | 399篇 |
1987年 | 381篇 |
1986年 | 349篇 |
1985年 | 362篇 |
1984年 | 340篇 |
1983年 | 267篇 |
1982年 | 244篇 |
1981年 | 190篇 |
1980年 | 191篇 |
1979年 | 304篇 |
1978年 | 190篇 |
1976年 | 197篇 |
1975年 | 191篇 |
1974年 | 224篇 |
1973年 | 207篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Serum catalase enzyme activity in liver diseases 总被引:1,自引:0,他引:1
Serum catalase activity was moderately increased in fatty liver, acute alcoholic hepatitis and in the decompensated form of cardiac circulatory failure. It showed significant increase in acute yellow atrophy and in toxic hepatitis while no changes were detected in liver cirrhosis and viral hepatitis. Serum catalase activity showed a good correlation (r = 0.820) with the serum glutamate dehydrogenase activity. In accordance with our results, the inexpensive assay of serum catalase activity is suggested for the detection of severe liver cell damage. 相似文献
82.
Calcium in hippocampus following lidocaine induced seizures: an electron cytochemical study 总被引:1,自引:0,他引:1
The effect of lidocaine seizures on cellular accumulation of calcium was studied in hippocampal subfields CA1 and CA3 and the dentate gyrus of rats, using the combined oxalate-pyroantimonate method. The specificity of the reaction was ascertained by EGTA treatment and X-ray microanalysis. In control rats, calcium was visualized between myelin lamellae of axons, in synaptic vesicles and in some lysosomes. Two hours after onset of lidocaine seizures selective neuronal degenerations appeared in hippocampal subfields CA1 and CA3 but not in the dentate gyrus. Calcium deposits were present in numerous mitochondria of pyramidal cells and, occasionally, also of neuroglial cells. Many of these mitochondria exhibited ultrastructural alterations. Calcium uptake was most prominent in the CA3 sector but was also present in the CA1 subfield as well as the dentate gyrus. Intracellular calcium uptake, in consequence, is not the unique attribute of selectively vulnerable hippocampal neurons. 相似文献
83.
Between 1981–83 the gut contents ofDaphnia galeata, D. cucullata, Eudiaptomus gracilis, andCyclops vicinus were examined with light and scanning electron microscope to obtain information on the feeding of these species in Lake Balaton.
The twoDaphnia species feed mainly on abioseston, and it is assumed that their primary nutrient source was organic matter adsorbed onto
the surfaces of the abioseston granules plus bacteria and detritus.E. gracilis feeds on algae, showing a preference for green algae and diatoms.C. vicinus is also a prodigious consumer of algae in Lake Balaton, utilizing the whole size spectrum of phytoplankton.
Concerning the trophic relationships between phytoplankton and zooplankton in Lake Balaton, that between diatoms and bothE. gracilis andC. vicinus is the most conspicouos. Convincing evidence for an extensive utilization of blue-green algae was not found. Though there
is no firm evidence yet, it is likely that theDaphnia are dependent on organic matter adsorbed on the abioseston. 相似文献
84.
López-Gatius F 《Theriogenology》1989,32(2):185-195
Two consecutive experiments were conducted. In Experiment 1, 24 Friesian lactating cows were randomly assigned to two groups. Cows in Group I received intramuscularly (i.m.) 500 mcg of cloprostenol, 1250 IU of human chorionic gonadotropin (hCG) and 5 mg of estradiol benzoate 12 h after cloprostenol treatment. Cows in Group II received 750 IU i.m. of hCG and 3 mg of estradiol benzoate 12 h after cloprostenol treatment. Treatment was given on Day 16 after estrus in both groups. All animals showed estrus within 24 to 48 h after cloprostenol treatment. The average interval from cloprostenol injection to the onset of estrus was not influenced by treatments. Four cows in Group I failed to ovulate and became cystic. In Experiment 2, 71 Friesian lactating cows were randomly assigned to two groups. Cows in Group I received 500 mcg i.m. of cloprostenol after corpus luteum detection by palpation per rectum. Cows in Group II received 500 mcg of cloprostenol plus 750 IU of hCG and 3 mg of estradiol benzoate 12 h after. When estrus ready for service was confirmed by rectal examination, cows were inseminated. The percentage of cows ready for service tended to be lower (P < 0.06) between cows in Group I (88%) and those in Group II (100%). The average interval from cloprostenol treatment to service was longest (P < 0.001) in Group I (78.7 h +/- 14.9, X +/- SD) vs Group II (48 h +/- 2.9). The degree of readiness for service synchrony was lowest (P < 0.001) in Group I (59.3%) vs Group II (94.2%). The pregnancy rates of cows synchronized or treated were not altered by hCG-estradiol benzoate treatment (P > 0.25). These results suggest that in dairy cows treated with cloprostenol following palpation per rectum of a corpus luteum and then with 750 IU of hCG and 3 mg of estradiol benzoate 12 h later, a single fixed-time insemination at 48 h after cloprostenol treatment should be performed. 相似文献
85.
G Csaba P Kovács V László 《Cellular and molecular biology, including cyto-enzymology》1989,35(5):511-514
Tetrahymena cells treated with insulin in mass cultures were separated to single-cell clones or one of the "sister-cells" of dividing Tetrahymena (in single-cell culture) was treated with insulin. In both cases the FITC-insulin binding of sister-cells were compared. The insulin imprinting significantly increased the insulin binding of cells. There was also a significant difference between the imprinted and not imprinted sisters as well as between the not imprinted sisters. This demonstrates the existence of a difference (in hormone binding) between sister-cells and justifies that the information of the first hormone treatment (imprinting) is not equally divided between the sister-cells. 相似文献
86.
87.
Fixed bacteria of the protein A-rich Cowan I Staphylococcus strain were labelled with fluorescein isothiocyanate and used as the second-step reagent in an indirect immunofluorescent assay of specific cell-surface antigen expression. The results are documented with fluorescence microscopy and flow cytometry. 相似文献
88.
The interaction between the Ca2+ transport ATPase and the proteolipid of rabbit sarcoplasmic reticulum was analyzed by fluorescence energy transfer, using the following donor: acceptor combinations: Ca2(+)-ATPase tryptophan----IAEDANS-proteolipid; IAEDANS-ATPase----IAF-proteolipid; IAEDANS-proteolipid----IAF-ATPase. The observed energy transfer may indicate weak interaction between the Ca2(+)-ATPase and proteolipid, but collisional energy transfer definitely contributes. The energy transfer was abolished by deoxycholate or sodium dodecylsulfate at concentrations sufficient to solubilize the membrane. In view of the low proteolipid content of sarcoplasmic reticulum and the weak interaction suggested by the energy transfer, at best only a small fraction of ATPase molecules could exist in the form of ATPase-proteolipid complexes. 相似文献
89.
The freshwater snail L. stagnalis is known to be able to respond to a strong, noxious stimulus with a full retraction of the foot and head into the shell accompanied with expelling the blood through the hemal pore. We have found that this behavioural response, besides graded local retractions, can be triggered by mild tactile stimulation provided that the stimulus is repeated several times. Only a complete exsanguination could be obtained, indicating that it is an all-or-none defensive behaviour. In an electrophysiological investigation of isolated brain, a number of similarities were found between this all-or-none behaviour and the so-called input 3 to central neurons, as described by Benjamin and Winlow. These include ability to be selectively activated by high calcium solutions, and blocked by keeping the snails in a spoiled water. Injection of snails with naloxone (0.5-2.0/micrograms/g) or ergotamine (0.4/microgram/g) blocked selectively the whole body withdrawal induced by tactile stimulation, but not that induced by injection of a high calcium saline or acetylcholine solution, indicating that enkephalinergic and/or dopaminergic mechanosensory neurons might be involved. The consideration of available data has led to a working hypothesis that the activity of input 3 might be the neurophysiological correlate of the high threshold all-or-none whole body withdrawal associated with exsanguination. 相似文献
90.
On the solution of mathematical models of herd immunity in human helminth infections 总被引:1,自引:0,他引:1
Marco V. José 《Journal of mathematical biology》1989,27(6):707-715
The general solution of the mathematical model of herd immunity to human helminth infections recently proposed by Anderson and May [3] is obtained. The numerical solution of a more accurate biological model is indistinguishable from the corresponding exact solution of a more tractable mathematical model. Computer simulations of some particular cases of this model support the notion that both ecological and immunological factors determine the observed convex patterns of age-prevalence and age-intensity curves of human helminth infections.This work was made thanks to the advise and support of Dr. Robert M. May while the author was Postdoctoral Fellow at Princeton University 相似文献