全文获取类型
收费全文 | 1266篇 |
免费 | 79篇 |
国内免费 | 5篇 |
专业分类
耳鼻咽喉 | 1篇 |
儿科学 | 49篇 |
妇产科学 | 60篇 |
基础医学 | 124篇 |
口腔科学 | 66篇 |
临床医学 | 110篇 |
内科学 | 299篇 |
皮肤病学 | 22篇 |
神经病学 | 61篇 |
特种医学 | 24篇 |
外科学 | 118篇 |
综合类 | 16篇 |
预防医学 | 52篇 |
眼科学 | 25篇 |
药学 | 85篇 |
中国医学 | 5篇 |
肿瘤学 | 233篇 |
出版年
2024年 | 3篇 |
2023年 | 8篇 |
2022年 | 22篇 |
2021年 | 51篇 |
2020年 | 28篇 |
2019年 | 34篇 |
2018年 | 33篇 |
2017年 | 24篇 |
2016年 | 27篇 |
2015年 | 40篇 |
2014年 | 55篇 |
2013年 | 63篇 |
2012年 | 101篇 |
2011年 | 135篇 |
2010年 | 78篇 |
2009年 | 45篇 |
2008年 | 66篇 |
2007年 | 78篇 |
2006年 | 56篇 |
2005年 | 49篇 |
2004年 | 57篇 |
2003年 | 66篇 |
2002年 | 51篇 |
2001年 | 32篇 |
2000年 | 22篇 |
1999年 | 23篇 |
1998年 | 15篇 |
1997年 | 6篇 |
1996年 | 5篇 |
1995年 | 5篇 |
1994年 | 7篇 |
1993年 | 7篇 |
1992年 | 8篇 |
1991年 | 2篇 |
1990年 | 4篇 |
1989年 | 4篇 |
1988年 | 2篇 |
1987年 | 4篇 |
1986年 | 7篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1973年 | 4篇 |
1972年 | 4篇 |
1971年 | 1篇 |
1970年 | 2篇 |
1966年 | 1篇 |
1954年 | 2篇 |
1938年 | 1篇 |
排序方式: 共有1350条查询结果,搜索用时 9 毫秒
1.
2.
3.
A1-adenosine receptors and associated guanine nucleotide-binding proteins (G proteins) have been co-purified from bovine cerebral cortex by agonist affinity chromatography [J. Biol. Chem. 264:14853-14859 (1989)]. In this study we have reconstituted purified bovine brain A1 receptors into human platelet membranes that contain A2- but no detectable A1-adenosine receptors. The recovery of reconstituted receptors was assessed from the binding of the antagonist radioligand [125I]3-(4-amino-3-iodo)phenethyl-1-propyl-8-cyclopentyl-xanthine and ranged from 32 to 84%. Coupling of reconstituted A1 receptors to platelet G proteins was evaluated by measurement of the high affinity binding of an agonist radioligand, 125I-aminobenzyladenosine, to receptor-G protein complexes and by stereospecific photoaffinity labeling of a 35,000-Da receptor polypeptide with the agonist photoaffinity label 125I-azidobenzyladenosine. Fifty percent of receptors reconstituted into platelet membranes bound agonists with high affinity, indicative of coupling to platelet G proteins. Reconstituted A1 receptors bound various ligands with affinities characteristic of A1 receptors of bovine brain. Although platelets contain both pertussis toxin-sensitive and -insensitive G proteins, reconstituted high affinity agonist binding was almost completely abolished by treatment of platelet membranes with guanosine 5'-3-O-(thio)triphosphate, pertussis toxin, N-ethylmaleimide, or heparin. Following reconstitution, A1 receptors could be resolubilized in complexes with platelet G proteins. The data suggest that marked species differences in the binding affinity of ligands to adenosine receptors result from differences in the receptors rather than membrane structure or G proteins and, further, that A1 receptors couple selectively and tightly to pertussis toxin-sensitive G proteins. 相似文献
4.
Malathion induced changes in the serum proteins and hematological parameters of an Indian catfish Heteropneustes fossilis (Bloch) 总被引:2,自引:0,他引:2
5.
6.
Ilia Frolov Vladimir Kleiner Boris Krentsel Robert Mardanov Kalyan Munshi Gennady Bukatov Vladimir Zakharov Sergey Sergeev 《Macromolecular chemistry and physics.》1993,194(8):2309-2321
In order to find out correlations between the structure of an external donor and the obtained polymer, the effects of different external donors on the activity and stereospecificity of the MgCl2/TiCl4 catalytic system in the bulk polymerization of 4-methyl-1-pentene (4MP) were carefully studied. Different silane compounds of the structure RnSi(OR')4-n (where: n = 1–3, R = alkyl/phenyl, R = alkyl) and Al(i-Bu)3 (TIBA) were used as external donors and cocatalyst, respectively. The effect of the donor/TIBA mole ratio on the activity and stereospecificity of the catalytic system was studied. Some major effects were observed for the three different external donors, namely, Me3Si(OMe), Me2Si(OMe)2, and Me3Si(OBu)3, in the 4MP polymerization process. It was observed that the effect of the external silane donor on the polymerization strongly depends upon the size of the alkoxy and hydrocarbon (alkyl/phenyl) groups which are attached to the silicon atom. A selective deactivation of the non-stereospecific centers, as well as a transformation of the non-stereospecific into isospecific centers, is assumed to occur. On the basis of the obtained results and literature data available for the propene polymerization, the concept of structural conformity between the ligand-surrounded active center and the monomer molecule was carried forward. 相似文献
7.
Detection by PCR and isolation assays of the anaerobic intestinal spirochete Brachyspira aalborgi from the feces of captive nonhuman primates 下载免费PDF全文
Munshi MA Taylor NM Mikosza AS Spencer PB Hampson DJ 《Journal of clinical microbiology》2003,41(3):1187-1191
The purpose of this study was to investigate the presence of the anaerobic intestinal spirochetes Brachyspira aalborgi and Brachyspira pilosicoli in the feces of captive nonhuman primates (n = 35) from 19 species housed at the Zoological Gardens, Perth, Western Australia. Both spirochete species are known to infect human beings. DNA was extracted from freshly collected feces with a commercially available QIAamp DNA stool minikit and subjected to PCR protocols amplifying portions of the 16S rRNA genes of the two spirochete species. The feces were also subjected to selective culture for the spirochetes. Subsequently, feces from 62 other captive animals or birds representing 39 species at the zoo were examined by PCR to determine whether they were reservoirs of infection. Six fecal samples from individuals from four primate species (two vervet monkeys, two Tonkean macaques, one Japanese macaque, and one hamadryas baboon) tested positive in the B. aalborgi PCR. B. aalborgi was not detected by PCR in any of the other animal or bird species tested, and B. pilosicoli was not detected in the primates or any of the other animals or birds. B. aalborgi was isolated from both PCR-positive vervet monkeys. This is the first time that B. aalborgi has been isolated from nonhuman primates and the first time that it has been isolated from the feces of any species. 相似文献
8.
Anupama Kohli MD Stephen P. Baker MCS MPH Nilima A. Patwardhan MD Ashraf Khan MD MRCPATH 《Endocrine pathology》1998,9(2):117-123
Previous studies have established that thyroid follicular neoplasms of higher malignant potential show a high p53 and low
bc1-2 expression. This however has not been well studied in Oncocytic (Hürthle cell) neoplasms, the management of which remains
controversial. We therefore studied the expression of p53 and bc1-2 in 18 Hürthle cell adenomas (HCA) and 8 Hürthle cell carcinomas
(HCC) and compared them with their benign and malignant counterparts, respectively, including 16 follicular adenomas (FA)
and 68 papillary carcinomas (PC). All 16 FA were bc1-2 positive, 4 were 2+, and 12 were 3+. On the other hand, 14/18 (78%)
HCA showed bc1-2 expression, 5 were 1+, 6 were 2+, and only 3 were 3_. Similarly, HCC showed a weaker bc1-2 staining pattern
compared to PC. Only 1 FA showed grade 1, p53 staining, the remaining 15 were negative, and 15/18 HCA showed p53 expression
of varying grades. This difference in p53 staining was statistically significant (p=0.005). A significant p53 overexpression was also seen in HCC compared to PC (p=0.005). In conclusion, there appears to be an inverse relationship between p53 and bc1-2 expression in thyroid follicular
neoplasms. A higher expression of p53 and lower levels bc1-2 in Hürthle cell neoplasms may have biological and clinical implications.
This may support a more aggressive surgical treatment for HCA compared to FA. 相似文献
9.
In the literature on fatigue testing of acrylic bone cements, data sets of various sizes have been used in different test series for the same cement formulation. There are two important consequences of this situation. First, it means that some test series last much longer than others, with all the implications for the cost of testing. Second, it makes drawing conclusions about the fatigue performance of a cement, based on the results of different literature series, a problematic issue. Clearly then, a recommendation as to what should be the minimum number of test specimens to use that would allow for confidence in the results of the statistical treatment of the test results (Gmin) would be desirable. In the present work, a method that could be used to culminate in such a recommendation is described. This method involves (i) obtaining experimental fatigue test results and (ii) analyzing those results using the Weibull probability distribution function and other statistical methods. This methodology is illustrated using fatigue life results obtained from uniaxial tension-compression fatigue tests on specimens fabricated from the polymerizing dough of one commercially available acrylic bone cement. For a tolerable error of 5%, we estimated Gmin to be either 7 (if the fatigue life results are treated using the two-parameter Weibull distribution function) or 11 (if the fatigue life results are treated using the three-parameter Weibull distribution function). To be on the conservative side, we therefore recommend that Gmin be 11. Three key limitations of the methodology presented here are discussed. 相似文献
10.
The human parvovirus B19 is now known to be one of the causative agents of nonimmune hydrops fetalis and spontaneous abortions in pregnant women. The presence of the viral proteins and antibodies in fetuses of B19-infected women suggests that the virus can cross the placental barrier. In order to gain an insight into the mechanism of intrauterine fetal infection and the virus-induced hydrops fetalis, we examined whether human umbilical cord blood cells were permissive for B19 replication. Cord blood cells were infected with B19 in vitro, and Southern blot analyses of low M(r) DNA isolated from these cells revealed the presence of the characteristic replicative intermediates of B19 DNA. In addition, B19 genome expression in cord blood cells was detected by Northern blot analysis. Quantitative DNA dot blot analysis of culture supernatants documented complete assembly and release of B19 progeny virions in these cells. The progeny virions were biologically active in secondary infections of normal human bone marrow cells. The human umbilical cord blood cells may be a useful alternative to bone marrow and fetal liver culture systems for further studies on B19 since the need for bone marrow donors is obviated and, unlike fetal tissues, there are no ethical questions associated with the experimental use of cord blood because it is normally discarded. These studies also suggest that the umbilical cord blood may be a site for active replication of parvovirus B19 in vivo and may thus provide a means for transmission of the virus during intrauterine fetal infections. 相似文献