全文获取类型
收费全文 | 3287篇 |
免费 | 196篇 |
国内免费 | 21篇 |
专业分类
耳鼻咽喉 | 12篇 |
儿科学 | 153篇 |
妇产科学 | 50篇 |
基础医学 | 356篇 |
口腔科学 | 118篇 |
临床医学 | 313篇 |
内科学 | 562篇 |
皮肤病学 | 50篇 |
神经病学 | 340篇 |
特种医学 | 250篇 |
外国民族医学 | 3篇 |
外科学 | 263篇 |
综合类 | 92篇 |
一般理论 | 1篇 |
预防医学 | 265篇 |
眼科学 | 103篇 |
药学 | 211篇 |
肿瘤学 | 362篇 |
出版年
2021年 | 17篇 |
2019年 | 22篇 |
2018年 | 37篇 |
2017年 | 22篇 |
2016年 | 30篇 |
2015年 | 36篇 |
2014年 | 44篇 |
2013年 | 83篇 |
2012年 | 86篇 |
2011年 | 107篇 |
2010年 | 81篇 |
2009年 | 77篇 |
2008年 | 147篇 |
2007年 | 162篇 |
2006年 | 177篇 |
2005年 | 142篇 |
2004年 | 140篇 |
2003年 | 135篇 |
2002年 | 112篇 |
2001年 | 99篇 |
2000年 | 110篇 |
1999年 | 90篇 |
1998年 | 54篇 |
1997年 | 61篇 |
1996年 | 60篇 |
1995年 | 41篇 |
1994年 | 28篇 |
1993年 | 50篇 |
1992年 | 86篇 |
1991年 | 79篇 |
1990年 | 79篇 |
1989年 | 96篇 |
1988年 | 67篇 |
1987年 | 67篇 |
1986年 | 72篇 |
1985年 | 66篇 |
1984年 | 72篇 |
1983年 | 51篇 |
1982年 | 32篇 |
1981年 | 28篇 |
1980年 | 45篇 |
1979年 | 59篇 |
1978年 | 38篇 |
1977年 | 24篇 |
1976年 | 23篇 |
1975年 | 28篇 |
1973年 | 26篇 |
1972年 | 23篇 |
1970年 | 20篇 |
1969年 | 28篇 |
排序方式: 共有3504条查询结果,搜索用时 15 毫秒
31.
Isolation, structure, and immunogenicity of Pseudomonas aeruginosa immunotype 4 high-molecular-weight polysaccharide. 总被引:3,自引:2,他引:3 下载免费PDF全文
A high-molecular-weight, immunogenic form of the lipopolysaccharide O side chain of Pseudomonas aeruginosa Fisher immunotype 4 (type 4, International Antigenic Typing System 1, Lanyi O:6) was isolated and characterized. Analysis by nuclear magnetic resonance spectroscopy confirmed the structural similarity of this high-molecular-weight polysaccharide and the type 4 O side chain. The polysaccharide was immunogenic in rabbits and mice, eliciting opsonophagocytic killing antibodies. Immunization with the polysaccharide produced significant protection against homologous challenge in both burned and granulocytopenic mice. Naturally acquired opsonic killing antibodies to type 4 polysaccharide were present in sera from unimmunized normal adults at levels comparable to postimmunization levels achieved after immunization with other type-specific polysaccharides. The specificity of the naturally occurring antibodies for the O side chain was documented by immunoblot analysis and inhibition studies. Naturally occurring polysaccharide-specific antibodies were comparable in their protective activity against live challenge in neutropenic animals to immunization-induced murine antibodies with similar specificity. These data suggest that naturally occurring serum antibody to P. aeruginosa type 4 lipopolysaccharide O side chains in most adults is not distinguishable in quantity or quality from immunization-induced antibodies in mice; evaluation of type 4-specific vaccines in humans may be complicated by this finding. 相似文献
32.
A study of the degree of progesterone support required for the maintenance
of various stages of pregnancy was undertaken in mice. Mated females were
ovariectomized at various stages of pregnancy and progesterone and
oestradiol support provided by s.c. Silastic implants with known release
characteristics. In the earliest stages of pregnancy (days 1-5), very low
concentrations of progesterone (<25% of normal physiological values)
were sufficient to maintain pre-implantation stages and allow implantation.
In the immediate post-implantation period (days 5-9), the development of
implantation sites and decidualization required considerably higher
progesterone support. In mid-pregnancy (days 11-14), progesterone alone
could not maintain pregnancy unless present in very high amounts; however,
the presence of oestradiol during this period lowered the progesterone
requirements to well within the physiological range. This effect of
oestradiol started on day 11 but required the level of oestradiol support
to be kept within strictly defined limits, with high concentrations
inducing abortion. Progesterone alone was able to maintain pregnancy from
day 15. These results indicate that the minimal progesterone support
required for pregnancy in mice varies considerably at different stages of
pregnancy and is at least partly modulated by oestradiol.
相似文献
33.
Isolation, Characterization, and Immunogenicity of Mycoplasma pneumoniae Membranes 总被引:3,自引:8,他引:3 下载免费PDF全文
Membrane and soluble fractions of Mycoplasma pneumoniae, M. pulmonis, and M. laidlawii B were prepared by hypotonic lysis of whole cells. The membranes of M. pneumoniae and M. laidlawii B contained, as percentage of dry weight: 34 to 37% protein, 59 to 61% lipid, 3 to 4% carbohydrate as hexose, and 0.2% ribonucleic acid as ribose. NADH2 and NADPH2 oxidase activities were localized in the soluble fractions of M. pneumoniae and in the membrane fraction of M. laidlawii B. NADH2 oxidase activity was localized in the soluble fraction of M. pulmonis. The lipids of M. pneumoniae were labeled when the organism was grown in the presence of either radioactive palmitic acid, oleic acid, cholesterol, or glycerol. The lipids were not labeled when grown in the presence of radioactive acetate. Palmitic acid radio-activity was found in neutral lipid, glycolipid, and phosphatide fractions. Immunodiffusion analyses of whole cells and membrane fractions demonstrated three reactive antigens. Two immunodiffusion antigens were localized in the membrane fraction. One of these apparently contains lipid. A third antigen, also considered lipoidal, was found in whole cells. Membrane and soluble fractions of M. pneumoniae were immunogenic. The immunogens eliciting metabolic-inhibiting antibodies were localized in the membrane. The membrane preparation also induced the formation of antibodies which fixed complement with an antigen extracted with lipid solvent. The soluble fraction contained a distinct immunogen which induces antibodies reactive in complement fixation with an antigen prepared by phenol extraction. 相似文献
34.
Mark H. Pollack Michael W. Otto Gary S. Sachs Andrew Leon M. Katherine Shear Joseph A. Deltito Martin B. Keller Jerrold F. Rosenbaum 《Journal of affective disorders》1994,30(4):273-281
This study examines clinical predictors of outcome for patients with panic disorder and depression in a 16 week, placebo-controlled trial of alprazolam and imipramine (n = 126). Baseline global severity of illness and phobic avoidance were differentially predictive of acute response to treatment. Patients in the mild to moderate range of global distress experienced smaller degrees of improvement on alprazolam than on imipramine at week 4. At endpoint, the relative effectiveness of the active medication versus placebo was diminished in patients with higher levels of phobic avoidance. This relationship was not evident for completers, suggesting that the adverse effects of avoidance on outcome after sustained treatment was reduced. 相似文献
35.
Recent experiments have shown that shortening and stretching of sarcomeres in single activated and unactivated myofibrils occur in stepwise fashion (Yang et al. (1998) Biophys J 74: 1473-1483; Blyakhman et al. (2001) Biophys J 81: 1093-1100; Yakovenko et al. (2002) Am J Physiol Cell Physiol 283: 735-742). Here, we carried out measurements on single myofibrils from rabbit psoas muscle to investigate steps in unactivated specimens in more detail. Activated and unactivated myofibrils were released and stretched in ramp-like fashion. The time course of length change in the single sarcomere was consistently stepwise. We found that in the unactivated myofibrils, step size depended on initial sarcomere length, diminishing progressively with increase of initial sarcomere length, whereas in the case of activated sarcomeres, step size was consistently 2.7 nm. 相似文献
36.
Isolation of a new clathrin heavy chain gene with muscle-specific expression from the region commonly deleted in velo-cardio-facial syndrome 总被引:3,自引:4,他引:3
Sirotkin H; Morrow B; DasGupta R; Goldberg R; Patanjali SR; Shi G; Cannizzaro L; Shprintzen R; Weissman SM; Kucherlapati R 《Human molecular genetics》1996,5(5):617-624
Velo-cardio-facial syndrome (VCFS) and DiGeorge syndrome (DGS) are
developmental disorders characterized by a spectrum of phenotypes including
velopharyngeal insufficiency, conotruncal heart defects and facial
dysmorphology among others. Eighty to eighty-five percent of VCFS/DGS
patients are hemizygous for a portion of chromosome 22. It is likely that
the genes encoded by this region play a role in the etiology of the
phenotypes associated with the disorders. Using a cDNA selection protocol,
we isolated a novel clathrin heavy chain cDNA (CLTD) from the VCFS/DGS
minimally deleted interval. The cDNA encodes a protein of 1638 amino acids.
CLTD shares significant homology, but is not identical to the ubiquitously
expressed clathrin heavy chain gene. The CLTD gene also shows a unique
pattern of expression, having its maximal level of expression in skeletal
muscle. Velopharyngeal insufficiency and muscle weakness are common
features of VCFS patients. Based on the location and expression pattern of
CLTD, we suggest hemizygosity at this locus may play a role in the etiology
of one of the VCFS-associated phenotypes.
相似文献
37.
W T Shearer J Ritz M J Finegold I C Guerra H M Rosenblatt D E Lewis M S Pollack L H Taber C V Sumaya F C Grumet 《The New England journal of medicine》1985,312(18):1151-1159
A 12-year-old boy with severe combined immunodeficiency who had been kept in a gnotobiotic environment since birth received bone marrow from a histoincompatible sibling in an attempt to reconstitute immunologic function. To prevent graft versus host disease, the donor's marrow was treated in vitro with monoclonal antibody and complement to remove alloreactive T cells. Eighty days after transplantation, the patient had a systemic illness characterized by fever, thrombocytopenia, gastrointestinal pain, and bleeding; he died on the 124th post-transplantation day. Postmortem examination revealed multiple tumor-like B-cell proliferations, recipient in origin, in numerous organs. Epstein-Barr virus (EBV) was isolated from the patient's pharyngeal secretions; EBV nuclear antigen was found in spontaneously transformed peripheral-blood lymphocytes, inflammatory cells from peritoneal fluid, and bone marrow cells; and EBV genomes were discovered in all tumor tissues. The donor's serum showed evidence of past EBV infection. Analysis of cellular immunoglobulin and immunoglobulin gene DNA from the tumors indicated both monoclonal and oligoclonal B-cell proliferations. These findings provide evidence for the evolution of EBV-induced polyclonal activation of B cells to oligoclonal B-cell proliferation and finally to monoclonal B-cell lymphoma. 相似文献
38.
Immunization with Pseudomonas aeruginosa high-molecular-weight polysaccharides prevents death from Pseudomonas burn infections in mice. 总被引:1,自引:1,他引:1 下载免费PDF全文
High-molecular-weight polysaccharides from the extracellular slime of Pseudomonas aeruginosa were evaluated as immunogens in Pseudomonas burn infections in mice. Immunization with immunotype 1 or 2 polysaccharides induced a strong immunotype-specific and weak cross-reactive antibody response but protected mice against burn infections caused by either immunotype. Passive protection was provided by rabbit antiserum to immunotype 1 polysaccharide against burn infection by the homologous organism. Pseudomonas high-molecular-weight polysaccharides are potentially effective vaccines in burn infections. 相似文献
39.
40.
Preparing monolayers of non-adherent mammalian cells 总被引:5,自引:0,他引:5
A simple method is described for preparing monolayers of non-adherent cells, using concanavalin A to bind the cells to wells of plastic microtest plates. The method was used successfully with all 202 human cell types tested, which included 23 tissue culture lines, 165 fresh specimens of all major histological types of leukemia and lymphoma, 20 fresh myelomas, 2 fresh thymomas, normal spleen and lymph node cells, fractionated T lymphocytes and B lymphocytes from peripheral blood, and cultured fetal amniotic cells. All cell types attached firmly, and were not detached by subsequent vigorous washing. In contrast, attempted attachment of cells in serum free medium, or with poly-L-lysine or glutaraldehyde, was ineffective with many cell types. We used the monolayers as target cells for antibodies to cell surface antigens, utilizing immune rosetting or complement-mediated cytotoxicity. This procedure should simplify most assays involving non-adherent target cells. 相似文献