首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   3654篇
  免费   274篇
  国内免费   12篇
耳鼻咽喉   19篇
儿科学   121篇
妇产科学   154篇
基础医学   487篇
口腔科学   79篇
临床医学   316篇
内科学   709篇
皮肤病学   25篇
神经病学   576篇
特种医学   246篇
外科学   443篇
综合类   85篇
一般理论   1篇
预防医学   225篇
眼科学   71篇
药学   207篇
中国医学   1篇
肿瘤学   175篇
  2021年   57篇
  2018年   33篇
  2017年   35篇
  2016年   44篇
  2015年   50篇
  2014年   64篇
  2013年   101篇
  2012年   119篇
  2011年   126篇
  2010年   86篇
  2009年   67篇
  2008年   134篇
  2007年   117篇
  2006年   181篇
  2005年   145篇
  2004年   132篇
  2003年   131篇
  2002年   118篇
  2001年   113篇
  2000年   118篇
  1999年   118篇
  1998年   67篇
  1997年   54篇
  1996年   53篇
  1995年   42篇
  1994年   49篇
  1993年   43篇
  1992年   111篇
  1991年   97篇
  1990年   96篇
  1989年   84篇
  1988年   76篇
  1987年   72篇
  1986年   77篇
  1985年   64篇
  1984年   63篇
  1983年   53篇
  1982年   46篇
  1981年   34篇
  1980年   45篇
  1979年   57篇
  1978年   47篇
  1977年   41篇
  1976年   52篇
  1975年   38篇
  1974年   47篇
  1973年   42篇
  1971年   35篇
  1970年   40篇
  1969年   31篇
排序方式: 共有3940条查询结果,搜索用时 15 毫秒
31.
32.
Several groups have reported an association between schizophrenia and the MscI polymorphism in the first exon of the dopamine D3 receptor gene (DRD3). We studied this polymorphism using a North American sample (117 patients plus 188 controls) and an Italian sample (97 patients plus 64 controls). In the first part of the study, we compared allele frequencies of schizophrenia patients and unmatched controls and observed a significant difference in the total sample (P = 0.01). The second part of the study involved a case control approach in which each schizophrenia patient was matched to a control of the same sex, and of similar age and ethnic background. The DRD3 allele frequencies of patients and controls revealed no significant difference between the two groups in the Italian (N = 53) or the North American (N = 54) matched populations; however, when these two matched samples were combined, a significant difference was observed (P = 0.026). Our results suggest that the MscI polymorphism may be associated with schizophrenia in the populations studied. © 1995 Wiley-Liss, Inc.  相似文献   
33.
X-linked spinal and bulbar muscular atrophy (SBMA) is caused by a CAG repeat expansion in the first exon of the androgen receptor (AR) gene. Disease-associated alleles (37-66 CAGs) change in length when transmitted from parents to offspring, with a significantly greater tendency to shift size when inherited paternally. As transgenic mice carrying human AR cDNAs with 45 and 66 CAG repeats do not display repeat instability, we attempted to model trinucleotide repeat instability by generating transgenic mice with yeast artificial chromosomes (YACs) carrying AR CAG repeat expansions in their genomic context. Studies of independent lines of AR YAC transgenic mice with CAG 45 alleles reveal intergenerational instability at an overall rate of approximately 10%. We also find that the 45 CAG repeat tracts are significantly more unstable with maternal transmission and as the transmitting mother ages. Of all the CAG/CTG repeat transgenic mice produced to date the AR YAC CAG 45 mice are unstable with the smallest trinucleotide repeat mutations, suggesting that the length threshold for repeat instability in the mouse may be lowered by including the appropriate flanking human DNA sequences. By sequence-tagged site content analysis and long range mapping we determined that one unstable transgenic line has integrated an approximately 70 kb segment of the AR locus due to fragmentation of the AR YAC. Identification of the cis - acting elements that permit CAG tract instability and the trans -acting factors that modulate repeat instability in the AR YAC CAG 45 mice may provide insights into the molecular basis of trinucleotide repeat instability in humans.   相似文献   
34.
BACKGROUND. Endoscopic sclerotherapy is an accepted treatment for bleeding esophageal varices, but it is associated with substantial local and systemic complications. Endoscopic ligation, a new form of endoscopic treatment for bleeding varices, may be safer. We compared the effectiveness and safety of the two techniques. METHODS. In this randomized trial we compared endoscopic sclerotherapy and endoscopic ligation in 129 patients with cirrhosis who had proved bleeding from esophageal varices. Sixty-five patients were treated with sclerotherapy, and 64 with ligation. Initial treatment for acute bleeding was followed by elective retreatment to eradicate varices. The patients were followed for a mean of 10 months, during which we determined the incidence of complications and recurrences of bleeding, the number of treatments needed to eradicate varices, and survival. RESULTS. Active bleeding at the first treatment was controlled by sclerotherapy in 10 of 13 patients (77 percent) and by ligation in 12 of 14 patients (86 percent). Slightly more sclerotherapy-treated patients had recurrent hemorrhage during the study (48 percent vs. 36 percent for the ligation-treated patients, P = 0.072). The eradication of varices required a lower mean (+/- SD) number of treatments with ligation (4 +/- 2 vs. 5 +/- 2, P = 0.056) than with sclerotherapy. The mortality rate was significantly higher in the sclerotherapy group (45 percent vs. 28 percent, P = 0.041), as was the rate of complications (22 percent vs. 2 percent, P less than 0.001). The complications of sclerotherapy were predominantly esophageal strictures, pneumonias, and other infections. CONCLUSIONS. Patients with cirrhosis who have bleeding esophageal varices have fewer treatment-related complications and better survival rates when they are treated by esophageal ligation than when they are treated by sclerotherapy.  相似文献   
35.
The factors governing in vitro basophil histamine release induced by radiocontrast material (RCM) were evaluated by the use of two RCMs (diatrizoate and metrizamide) and three structural analogs of RCM (benzoic acid, diaminobenzoic acid, and 3-acetamidobenzoic acid) in basophil histamine-release studies. Diatrizoate was chosen because it is a commonly used RCM and is routinely administered as a hypertonic drug (958 mOsm/kg or greater). Metrizamide is a newly synthesized RCM and is routinely administered in isotonic form (approximately 280 mOsm/kg). The analogs were used in hope of identifying any structure-function relationship that might exist between RCMs and the activation of a proposed basophil membrane receptor responsible for the induction of de granulation. In addition, results in a control group of normal subjects were compared with those in a group of patients who had experienced anaphylactoid reactions to intravenous RCM. Basophils from both groups were incubated with diatrizoate and metrizamide to assess their relative sensitivity to these drugs. Both metrizamide and diatrizoate induced in vitro histamine release. Therefore hypertonicity is not an absolute requirement for RCM-induced in vitro basophil de granulation. Although there was a trend far reagents without a prosthetic group at position 5 on the benzene ring (especially 3-acetamidobenzoic acid) to induce more release of histamine than reagents with such a prosthetic group, differences between these reagents did not reach statistical significance. Therefore no clearcut structure-function relationship could be demonstrated. “Reactor” subjects released significantly-larger percents of their intracellular histamine than did “nonreactors” (p < 0.05). Degranulated cells retained their ability to exclude trypan blue, an observation suggesting that RCM-induced histamine release does not involve cell death.  相似文献   
36.
Gamma interferon (IFN-gamma) has multiple immunomodulating effects and has been postulated as a possible immunopotentiating agent for the prevention or treatment of neonatal infections. This report describes the effect of rat recombinant IFN-gamma on the oxidative burst activity and CD11b expression of neonatal and adult rat polymorphonuclear leukocytes (PMNL). Oxidative burst activity was assessed by chemiluminescence and dihydrorhodamine flow cytometry. Neonatal PMNL exhibited significantly less oxidative burst activity than did adult PMNL. IFN-gamma mildly enhanced the chemiluminescence response of PMNL from both the rat pups and adults, but this effect was not statistically significant when analyzed by a multivariate model of repeated-measures analysis of variance for both chemiluminescence and dihydrorhodamine flow cytometry. CD11b expression was also not significantly enhanced by IFN-gamma.  相似文献   
37.
38.
Insemination with donor spermatozoa is an integral part of infertility treatment. For the last 3 years in our unit, intrauterine insemination with donor spermatozoa (IUID) has been used in preference to vaginal insemination. In this retrospective study, patients were offered an initial course of five single intrauterine inseminations with cryopreserved donor spermatozoa and treatment was then reviewed. A total of 389 patients received 1465 inseminations. In all, 1119 cycles were monitored using luteinizing hormone serum analyses and 346 cycles using the urine home test kits. The clinical pregnancy rate per insemination for the cycles monitored by the serum assay was 18.0% (202/1119) compared with the urine cycles (13.7%, 46/346) (P <05). The pregnancy loss rate was not significantly different (14.4%, 29/202 and 21.7%, 10/46) (serum and urine cycles respectively). The viable clinical pregnancy rate was significantly higher (P <03) for the serum cycles than for the cycles using the urinary monitoring (15.5%, 173/1119 and 10.4%, 36/346 respectively). The cycles monitored by serum assay had a significantly higher cumulative viable clinical pregnancy rate (P <0001) of 70.2% after nine inseminations compared with the urine monitored cycles of 54.8%. The majority of patients opted for the serum cycles, with a minority self-selecting the urine cycles mainly for travelling convenience. The explanation for the significant differences between the viable clinical pregnancy rates per insemination and the cumulative viable clinical pregnancy rates may be due to the sensitivity of the urine home test kit or the patients' interpretation of the result.   相似文献   
39.
The aims of this study were twofold: (i) to test for possible associations between serological evidence of acute Simkania negevensis (Sn) infection and acute exacerbation of chronic obstructive pulmonary disease and (ii) to examine the prevalence of past infections with Sn in patients with chronic obstructive pulmonary disease. In 120 patients (63%) there was serological evidence of past infection with Sn, which was not significantly different from the rate in a control population. In five hospitalizations serological evidence existed of acute infection with Sn around the time of the exacerbation of chronic obstructive pulmonary disease. In four of these cases, there was serological evidence of acute infection with at least one other respiratory pathogen. It is concluded that Sn can be associated serologically with exacerbation of chronic obstructive pulmonary disease, in most cases together with other respiratory pathogens. The implications of these findings should be investigated further. Electronic Publication  相似文献   
40.
Fluocortin butyl (FCB) is a newly synthesized corticosteroid with a high ratio of topical to systemic activity. FCB was studied in a multi-center, double-blind, placebo-controlled trial of therapy of perennial rhinitis. The study was conducted between January and May 1981. Patients evaluated suffered from either chronic allergic or chronic nonallergic rhinitis or both. A total of 306 patients from 16 investigative centers were evaluated by comparing FCB to placebo. Three separate dosage regimens were employed. Patients received a total daily dose of 2, 4, or 8 mg. FCB was found to be an effective therapeutic agent. It reduced symptoms of nasal congestion, rhinorrhea, postnasal drainage, and sneezing. It also markedly reduced the use of concomitant medications (chlorpheniramine maleate and/or pseudoephedrine). Relief of symptoms was noted as early as the first week of therapy, and the degree of improvement increased progressively during the study. There was little difference between the relief produced by the 4 mg and 8 mg regimens. Both of these were superior to the 2 mg regimen. The drug was well tolerated; no significant side effects were noted.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号