全文获取类型
收费全文 | 40781篇 |
免费 | 2480篇 |
国内免费 | 5篇 |
专业分类
43266篇 |
出版年
2023年 | 245篇 |
2022年 | 210篇 |
2021年 | 520篇 |
2020年 | 454篇 |
2019年 | 475篇 |
2018年 | 1226篇 |
2017年 | 1060篇 |
2016年 | 1461篇 |
2015年 | 1971篇 |
2014年 | 1972篇 |
2013年 | 2631篇 |
2012年 | 3027篇 |
2011年 | 2726篇 |
2010年 | 1734篇 |
2009年 | 1295篇 |
2008年 | 2055篇 |
2007年 | 2032篇 |
2006年 | 2008篇 |
2005年 | 1677篇 |
2004年 | 1666篇 |
2003年 | 1489篇 |
2002年 | 1403篇 |
2001年 | 1011篇 |
2000年 | 973篇 |
1999年 | 759篇 |
1998年 | 298篇 |
1997年 | 195篇 |
1996年 | 208篇 |
1995年 | 216篇 |
1994年 | 161篇 |
1992年 | 445篇 |
1991年 | 386篇 |
1990年 | 366篇 |
1989年 | 357篇 |
1988年 | 318篇 |
1987年 | 314篇 |
1986年 | 286篇 |
1985年 | 281篇 |
1984年 | 221篇 |
1983年 | 200篇 |
1982年 | 159篇 |
1979年 | 248篇 |
1978年 | 143篇 |
1974年 | 174篇 |
1973年 | 169篇 |
1972年 | 162篇 |
1971年 | 150篇 |
1970年 | 159篇 |
1969年 | 159篇 |
1968年 | 151篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
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
102.
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
103.
T Skórski M Kawalec J Kawiak 《Folia histochemica et cytobiologica / Polish Academy of Sciences, Polish Histochemical and Cytochemical Society》1987,25(1):23-27
The composition of peritoneal exudate and spleen cells of CD2F1 mice after fourfold i.p. administration of L 1210 leukemia cells treated with cyclophosphamide (L 1210-CY cells) were examined. The number of cells in peritoneal cavity did not increase, however, the spleen weight rose after administration of L 1210-CY cells. The per cent of lymphocytes T was increased 2.5 times but the content of macrophages and lymphocytes B was normal in the peritoneal cavity after L 1210-CY cells injections. In the spleen an 1.4 times increase of the per cent of lymphocytes B, but normal level of macrophages and lymphocytes T were observed. 相似文献
104.
Several mediators appear to interact in neurogenic inflammation 总被引:1,自引:0,他引:1
Plasma protein extravasation was studied in the rat abdominal skin. Substance P (SP), neurokinin A (NKA) and B (NKB) were found to induce extravasation with a threshold dose of about 1 pmol. Calcitonin gene-related peptide (CGRP) caused no or little extravasation alone but it potentiated the action of SP, NKA, NKB, and physalaemin. The potentiation of the SP-induced extravasation was unaffected by pretreatment with capsaicin, indomethacin or compound 48/80, it was reduced by neuropeptide Y or pretreatment with mepyramine plus cimetidine, and was abolished in streptozotocin diabetic rats. CGRP augmented extravasation induced by histamine, reduced the effect of ATP or adenosine and did not alter extravasation by serotonin, bradykinin or neurotensin. These results indicate that in addition to SP the novel mammalian tachykinins NKA and NKB may be considered as mediator candidates for neurogenic plasma extravasation. CGRP is a possible mediator of antidromic vasodilation. Furthermore, CGRP potentiates the extravasation caused by coexisting tachykinins and could thereby augment neurogenic inflammation. The diverse interactions of CGRP with other inflammatory mediators suggest multiple sites of action. 相似文献
105.
Changes in the serum cortisol level of maternal venous, umbilical venous and umbilical arterial blood were studied separately between the 28th-36th weeks in cases of preterm deliveries (n = 74) and in the 40th week in cases of term delivery (n = 34). Results indicate that between the 28th-40th weeks of pregnancy the cortisol concentration increased only in the serum of the umbilical artery; the "umbilical arterial/umbilical venous concentration X100" quotient rose from a value of 86% measured at 28th-32nd weeks to 103% in the 40th week of pregnancy. Positive correlation was found between the cortisol concentration of the three samples. On the basis of these results the authors believe that fetal adreno-cortical activity increases before birth. 相似文献
106.
Antibacterial, antifungal and antiprotozoal effects of nine mono- and bishydrazones of glycolaldehyde, glyoxal, methoxyacetaldehyde
and glutaraldehyde were studied using eight model organisms. It was found that bishydrazones are much more efficient antimicrobial
agents than monohydrazones in the case of all model microorganisms. 相似文献
107.
Serum gastrin and gastric acid secretion at high altitude 总被引:1,自引:0,他引:1
N Jó O García R Jara F Garmendia A Nago R García H Hidalgo L Flores 《Hormones et métabolisme》1987,19(4):182-183
108.
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
109.
Weekly sampling and simultaneous measurements of temperature, pH, and conductivity were made at three stations in the reedbelt,
between 1980–82. 20 cladoceran and 14 copepod species were encountered, of whichCyclops vicinus vicinus was found in the lake for the first time. Of the measured environmental features, temperature showed the greatest seasonal
changes; pH and conductivity were less variable. There were, both quantitatively and qualitatively, constant differences between
the three stations, although they lay close to each other. 相似文献
110.
S Rojo P Aparicio S Y Choo J A Hansen J A López de Castro 《Journal of immunology (Baltimore, Md. : 1950)》1987,139(3):831-836
The structure of a new HLA-B27 variant, B27f, distinguishable from other HLA-B27 subtypes by isoelectric focusing and serologic criteria, has been established by comparative peptide mapping and radiochemical sequence analysis. HLA-B27f differs from the major B27.1 subtype in three clustered amino acid replacements: Asp74, Asp77, and Leu81 in B27.1 are changed to Tyr74, Asn77, and Ala81, respectively in B27f. This pattern of differences is analogous to that of HLA-B27.2 in that this subtype also differs from B27.1 in multiple clustered substitutions within the same segment. Thus, polymorphism within the HLA-B27 system is being achieved by introducing different sets of amino acid changes within a particular short segment of the alpha 1 domain. The most likely mechanism for the introduction of multiple changes within this segment is a nonreciprocal recombination event, such as gene conversion. The structural analogies and ethnic distribution of B27f and B27.2 as compared with those of B27.3, and B27.4 support a dynamic model of HLA-B27 evolution in which polymorphism has been created after the separation of the major ethnic groups. In this model, a Caucasian branch would be characterized by subtypes differing from B27.1 in a few changes within the alpha 1 domain, which were probably generated by single genetic steps. An Oriental branch would include those subtypes which differ from B27.1 by changes in both alpha 1 and alpha 2, involving multiple genetic steps for their generation. 相似文献