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   1588篇
  免费   147篇
  国内免费   5篇
耳鼻咽喉   10篇
儿科学   78篇
妇产科学   28篇
基础医学   200篇
口腔科学   24篇
临床医学   163篇
内科学   299篇
皮肤病学   5篇
神经病学   115篇
特种医学   196篇
外科学   218篇
综合类   66篇
预防医学   148篇
眼科学   25篇
药学   98篇
中国医学   1篇
肿瘤学   66篇
  2022年   13篇
  2021年   13篇
  2019年   19篇
  2018年   34篇
  2017年   22篇
  2016年   20篇
  2015年   27篇
  2014年   45篇
  2013年   57篇
  2012年   46篇
  2011年   47篇
  2010年   40篇
  2009年   23篇
  2008年   52篇
  2007年   53篇
  2006年   49篇
  2005年   55篇
  2004年   47篇
  2003年   40篇
  2002年   35篇
  2001年   43篇
  2000年   30篇
  1999年   41篇
  1998年   45篇
  1997年   39篇
  1996年   38篇
  1995年   38篇
  1994年   38篇
  1993年   28篇
  1992年   26篇
  1991年   35篇
  1990年   38篇
  1989年   48篇
  1988年   50篇
  1987年   40篇
  1986年   43篇
  1985年   42篇
  1984年   27篇
  1983年   28篇
  1982年   12篇
  1981年   21篇
  1980年   14篇
  1979年   15篇
  1978年   16篇
  1977年   13篇
  1976年   17篇
  1975年   17篇
  1974年   20篇
  1973年   15篇
  1972年   16篇
排序方式: 共有1740条查询结果,搜索用时 0 毫秒
1.
The authors examined the possibility that ethane 1,2-dimethanesulphonate (EDS) has a cytotoxic effect on spermatogenesis that is not secondary to androgen withdrawal resulting from the well known cytotoxic effect of EDS on Leydig cells. Adult male rats were implanted with polydimethylsiloxane (PDS) capsules containing testosterone (T) and estradiol (E), and were simultaneously injected with EDS. The PDS-TE implants, by inhibiting luteinizing hormone (LH) production, prevented Leydig cells from repopulating the testis and clamped testosterone within the seminiferous tubules at increasing concentrations relative to implant size. In rats that received EDS alone, the number of advanced spermatids per testis was significantly reduced by 2 weeks, but within 8 weeks returned to the numbers maintained in vehicle-injected control rats or in vehicle-injected rats that received testosterone- and estradiol-filled capsules of 24 cm and 0.1 cm, respectively (PDS-24TE). Surprisingly, in rats that received an EDS injection plus PDS-24TE implants, the number of advanced spermatids per testis was significantly reduced at 8 weeks and severe seminiferous tubule atrophy occurred despite the fact that the testosterone concentration was sufficient to quantitatively maintain spermatogenesis in vehicle-injected rats. In rats injected with EDS and implanted with 24 cm testosterone but not estradiol-filled capsules (PDS-24T), the advanced spermatid number per testis was significantly higher than that in the EDS plus PDS-24TE rats, but significantly lower than that in control rats. These results suggest that EDS may have a cytotoxic effect on the seminiferous epithelium that is independent of the elimination of Leydig cells, and the EDS and estradiol act synergistically to exert a profound toxic effect on spermatogenesis.  相似文献   
2.
We examined determinants of nonvertebral fracture in elderly men from six U.S. communities followed an average of 4.1 years. Six clinical risk factors predicted fracture risk independent of hip BMD: tricyclic antidepressant use, previous fracture, inability to complete a narrow walk trial, falls in previous year, age > or =80 years, and depressed mood. INTRODUCTION: There are few prospective studies of fracture determinants in men. We examined the associations between a comprehensive set of clinical risk factors and risk of nonspine fracture in older men and whether determinants of fracture risk were independent of total hip BMD. MATERIALS AND METHODS: A total of 5995 men > or =65 years of age were recruited from six communities in the Unites States and followed prospectively for an average of 4.1 years. Baseline assessments of demographic, lifestyle, medical history, functional status, anthropometry, and cognitive, visual, and neuromuscular function were assessed by questionnaire or examination. Triannual mailed questionnaires ascertained incident fracture; reported fractures were adjudicated by physicians using medical records and X-ray reports. Proportional hazards models were used to develop multivariable models, selecting variables and controlling for BMD. RESULTS: Of 5876 men, 4.7% (N = 275) reported an incident nonspine fracture during follow-up (11.46/1000 person-years). Tricyclic antidepressant use (hazard ratio [HR], 2.36; 95% CI, 1.25-4.46), history of fracture at or after age 50 (HR, 2.07; 95% CI, 1.62-2.65), inability to complete a narrow walk trial (HR, 1.70; 95% CI, 1.23-2.34), falls in previous year (HR, 1.59; 95% CI, 1.23-2.05), age > or =80 years (HR, 1.33; 95% CI, 1.01-1.76), depressed mood (HR, 1.72; 95% CI, 1.00-2.95), and decreased total hip BMD (HR, 1.53; 95% CI, 1.34-1.74) were independently related to increased risk. Compared with having none (48.0% of men), having three or more of the clinical risk factors (4.9% of men) increased fracture risk 5-fold, independent of BMD. Having three or more risk factors and being in the lowest tertile of BMD was associated with a 15-fold greater risk than having no risk factors and being in the highest BMD tertile. CONCLUSIONS: Several clinical risk factors were independently associated with nonspine fractures in elderly men. The combination of multiple risk factors and low BMD was a very powerful indicator of fracture risk.  相似文献   
3.
The antineoplastic properties of suramin, a polyanionic agent with demonstrated antigrowth factor activity, are under evaluation in vitro, in vivo, and in clinical trials. Suramin has been shown to have antitumor activity in patients with advanced, hormone refractory prostate cancer. During these trials, significant resolution of osseous pain was observed in nearly three quarters of the patients treated with suramin. To evaluate the effect of suramin on bone cells, we studied the effect of suramin on bone resorption in a neonatal mouse calvarial assay. Suramin inhibited bone-resorbing activity in a dose-related fashion and had an additive effect with calcitonin. Calvaria pretreated with suramin had less bone-resorbing activity, fewer attached osteoblasts, and less medium alkaline phosphatase activity than control calvaria. Suramin also inhibited osteoclastic release of tritiated proline from labeled bone in a dose-dependent fashion. The effect of metastatic prostate carcinoma on bone is incompletely understood, but may be moderated by tumor-produced factors and/or cytokines. The effects of several such agents, therefore, were examined in combination with suramin. Bone resorption induced by PTH, epidermal growth factor, tumor necrosis factor, and a tumor-produced factor, PTH related-protein, was blocked by suramin. The ability of suramin to inhibit the bone-resorbing effects of several cytokines suggests that its mechanism may involve direct action on bone metabolism. Autoradiography performed on calvaria treated with labeled suramin demonstrated heavy deposition of suramin on the outer surface of the matrix, adjacent to osteoblasts and osteoclasts lining the outer table, suggesting that bone cells may be subject to high local concentrations of the drug, in keeping with this hypothesis.  相似文献   
4.
Visual assessment of urethrovesical junction mobility   总被引:1,自引:1,他引:0  
The aim of the study was to compare visual assessment of anterior vaginal wall descent with the Q-tip test in evaluating urethrovesical junction mobility. One hundred and eleven patients with prolapse and/or urinary incontinence were examined in the supine lithotomy position with an empty bladder. Maximum straining Q-tip tests and maximum descent of the anterior vaginal wall were measured. Using each centimeter of descent as a cutoff value, the sensitivities, specificities and positive and negative predictive values were compared to those of the Q-tip test. As the cutt-off points were moved distally, specificity increased at the expense of sensitivity. There was no single cut-off point that provided adequate sensitivity and specificity to be clinically useful to replace the Q-tip test. It was concluded that visual assessment of anterior vaginal wall descent does not provide diagnostic accuracy and acceptable sensitivity and specificity to determine urethrovesical junction mobility. Other methods should be employed to assess support.Editorial Comment: Many clinicians claim that they can assess urethrovesical junction mobility visually and thus avoid employing other means, such as the Q-tip test, ultrasonography, bead-chain cystography or fluoroscopy. Montella et al. evaluate a technique of visual assessment of urethrovesical junction mobility based on the International Continence Society's Standardization of Terminology of Female Organ Prolapse and Pelvic Floor Dysfunction as compared to evaluation with the Q-tip test. Their results clearly indicate that this technique (measurement of the descent of point Aa) does not provide adequate sensitivity or specificity in determining urethrovesical junction descent compared to the Q-tip test. Although this technique was only compared to the Q-tip test and not all other modalities available, it is doubtful that visual assessment of anterior wall descent at any level would correspond to urethrovesical junction mobility, as is discussed very succinctly by the authors.  相似文献   
5.
目的:对临床确诊糖尿病患同时测定血清葡萄糖(Glu)及糖化血清蛋白(GSP)的含量,观察二的关系,以及糖化血清蛋白水平对于评价近期(2—3周)糖尿病患血糖在体内变化的临床意义进行了观察。方法:血清葡萄糖、糖化血清蛋白测定均采用酶法测定。结果:178例糖尿病患Glu、GSP均正常3l例占17.4%;Glu、GSP均增高107例占60.1%;Glu正常、GSP增高15例占8.43%;Glu增高、GSP正常25例占14%。结论:糖化血清蛋白的含量不受即时血糖的影响,二的变化不成比例性,对评价糖尿病患2~3周病情的控制是一项灵敏可靠的指标,尤其对于住院病人的治疗与监控有一定的意义。  相似文献   
6.
7.
8.
9.
Abstract This study illustrates how the Total Life Concept (TLC) program originated by AT&T was successfully transplanted to another work site, Sandia National Laboratories. Demographics of the participants at A T&T and Sandia differ and make comparisons difficult, but it is possible to assess program impact in terms of participation rates for each program. The original AT&T TLC pilot study had three major components: orientation, testing, and risk interpretation; lifestyle-improvement courses; and activities to promote health. Sandia kept the three major components of the AT&T TLC concept and made some modifications to meet Sandia's needs. Sandia's experience of adopting a model program and tailoring it to local needs worked well, demonstrating that an existing model can be successfully altered to meet the needs of different companies in varied settings.  相似文献   
10.
Steroid 21-hydroxylase deficiency is among the most common inborn errors of metabolism in man. Characterization of mutations in the 21- hydroxylase gene (CYP21) has permitted genetic diagnosis, facilitated by the polymerase chain reaction (PCR). The most common mutation is conversion of an A or C at nt656 to a G in the second intron causing aberrant splicing of mRNA. Homozygosity for nt656G is associated with profoundly deficient adrenal cortisol and aldosterone synthesis, secondary hypersecretion of adrenal androgens, and a severe form of congenital adrenal hyperplasia (CAH) characterized by ambiguous genitalia and/or sodium wasting in newborns. During the course of genetic analysis of CYP21 mutations in CAH families, we and others have noticed a number of relatives genotyped as nt656G homozygotes, yet showing no clinical signs of disease. A number of lines of evidence have led us to propose that the putative asymptomatic nt656G/G individuals are incorrectly typed due to dropout of one haplotype during PCR amplification of CYP21. For prenatal diagnosis, we recommend that microsatellite typing be used as a supplement to CYP21 genotyping in order to resolve ambiguities at nt656.   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