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   9011篇
  免费   804篇
  国内免费   18篇
耳鼻咽喉   43篇
儿科学   246篇
妇产科学   124篇
基础医学   1099篇
口腔科学   340篇
临床医学   1063篇
内科学   2107篇
皮肤病学   110篇
神经病学   637篇
特种医学   367篇
外科学   1238篇
综合类   130篇
一般理论   5篇
预防医学   934篇
眼科学   152篇
药学   722篇
中国医学   14篇
肿瘤学   502篇
  2023年   38篇
  2022年   70篇
  2021年   175篇
  2020年   86篇
  2019年   165篇
  2018年   210篇
  2017年   160篇
  2016年   174篇
  2015年   186篇
  2014年   273篇
  2013年   391篇
  2012年   557篇
  2011年   543篇
  2010年   313篇
  2009年   325篇
  2008年   466篇
  2007年   486篇
  2006年   479篇
  2005年   463篇
  2004年   459篇
  2003年   362篇
  2002年   419篇
  2001年   158篇
  2000年   142篇
  1999年   185篇
  1998年   109篇
  1997年   123篇
  1996年   102篇
  1995年   93篇
  1994年   85篇
  1993年   78篇
  1992年   119篇
  1991年   110篇
  1990年   105篇
  1989年   119篇
  1988年   107篇
  1987年   108篇
  1986年   100篇
  1985年   95篇
  1984年   93篇
  1983年   86篇
  1982年   84篇
  1981年   79篇
  1980年   50篇
  1979年   69篇
  1978年   48篇
  1977年   50篇
  1976年   54篇
  1974年   48篇
  1972年   38篇
排序方式: 共有9833条查询结果,搜索用时 15 毫秒
1.
ObjectiveIdentify factors associated with healthcare providers' frequency of depot medroxyprogesterone acetate (DMPA) provision to adolescents.Study designWe analyzed data from surveys mailed to a nationally representative sample of public-sector providers and office-based physicians (n=1984). We estimated adjusted odds ratios (aORs) and 95% confidence intervals (CIs) of factors associated with frequent DMPA provision to adolescents in the past year.ResultsAlthough most providers (>95%) considered DMPA safe for adolescents, fewer reported frequent provision (89% of public-sector providers; 64% of office-based physicians). Among public-sector providers, factors associated with lower odds of frequent provision included working in settings without Title X funding (aOR 0.44, 95% CI 0.30–0.64), reporting primary care as their primary clinical focus versus reproductive or adolescent health (aOR 0.42, 95% CI 0.28–0.61), and providing fewer patients with family planning services. Among office-based physicians, factors associated with lower odds of frequent provision included specializing in obstetrics/gynecology (aOR 0.50, 95% CI 0.27–0.91) and family medicine (aOR 0.21, 95% CI 0.09–0.47) versus adolescent medicine, completing training ≥15 versus <5 years ago (aOR 0.27, 95% CI 0.09–0.83), and reporting that 0–24% of patients pay with Medicaid or other government healthcare assistance versus ≥50% (aOR 0.23, 95% CI 0.09–0.61). The reason most commonly reported by providers for infrequent DMPA provision was patient preference for another method.ConclusionsWhile most providers reported frequently providing DMPA to adolescents, training on evidence-based recommendations for contraception, focused on subgroups of providers with lower odds of frequent DMPA provision, may increase adolescents' access to contraception.ImplicationsAlthough >95% of providers considered depot medroxyprogesterone (DMPA) a safe contraceptive for adolescents, only 89% of public-sector providers and 64% of office-based physicians reported frequently providing DMPA to adolescents. Provider training on evidence-based recommendations for contraception counseling and provision may increase adolescents' access to DMPA and all methods of contraception.  相似文献   
2.
3.
4.
Background and Aims: Gastric antral vascular ectasia (GAVE) is commonly found in patients with cirrhosis, but it is also associated with other diseases in the absence of cirrhosis. Whether GAVE confers a different severity of gastrointestinal (GI) bleeding between patients with and without cirrhosis remains unknown. We aim to examine whether there is a difference in clinically significant GI bleeding due to GAVE in patients with or without cirrhosis. Methods: This is a retrospective case-control study of patients who were diagnosed with GAVE between January 2000 and June 2014. Patients were categorized into cirrhosis and noncirrhosis groups, and those with an additional GI bleeding source were excluded. Univariate comparisons and multivariable models were constructed using logistic regression. Results: In total, 110 patients diagnosed with GAVE on esophagogastroduodenoscopy (EGD) were included in our analysis; 84 patients had cirrhosis (76.4%) and 26 (23.6%) did not. Active GI bleeding was more prevalent in patients without cirrhosis (63.4% vs. 32.1%, p=0.003) despite similar indications for EGD, and endoscopic treatment with argon plasma coagulation (APC) was required more often in this group, approaching statistical significance (27% vs. 10.7%, p=0.056). There was no difference in bleeding severity, as evidenced by similar re-bleeding rates, surgery, or death attributed to uncontrolled bleeding. The strongest independent risk factor for GI bleeding was the absence of cirrhosis (odds ratio (OR): 5.151 (95% confidence interval (CI): 1.08-24.48, p=0.039). Conclusions: Patients with GAVE in the absence of cirrhosis are at higher risk for active GI bleeding and require more frequent endoscopic treatment than similar patients with cirrhosis. It may be worthwhile to treat GAVE in this population even in the absence of active bleeding.  相似文献   
5.
6.
Medical therapy is currently the most popular treatment choice for lower urinary tract symptoms (LUTS) associated with benign prostatic hyperplasia (BPH). Because medical therapy of BPH-related LUTS is considered a life-long strategy, short- and long-term cost considerations should play a major role in therapeutic decision-making. The effectiveness in terms of long and short amelioration of symptoms, flow rate, and quality of life are well documented for 5α-blockers and 5α-reductase inhibitors as well as for the gold standard treatment for BPH, transurethral resection of the prostate and minimally invasive therapies. Short-and long-term safety concerns also are well documented for these various treatment options. On the contrary, short- and long-term costs have been less well studied and comparisons depend on the model or analyses undertaken in the few studies available. However, the economic studies based on prospective clinical trial data that have become available throughout the past several decades allow us to rationalize our use of α-blockers, 5α -reductase inhibitors, and combination therapy, taking into consideration age, severity of symptoms, prostate volume, prostate-specific antigen, and the differential response of the various medications (and combination) in selected patients. Based on current studies, 5α -blockers generally provide cost-effective therapy for most patients, whereas 5α-reductase therapy and combination therapy provide cost-effective treatment for patients with larger prostate glands or higher baseline prostate-specific antigen levels.  相似文献   
7.
8.
9.
Ruggieri  PM; Laub  GA; Masaryk  TJ; Modic  MT 《Radiology》1989,171(3):785-791
The technique and feasibility of magnetic resonance (MR) angiography of intracranial vessels were studied in 35 healthy volunteers. Variations in image orientation, repetition time (TR), and flip angle were evaluated to determine their effects on flow-related enhancement. Gradient modifications--including echo time (TE), motion compensation, bandwidth, and field of view--were also studied in an effort to reduce motion-induced phase shifts. Results indicated that a FISP (fast imaging with steady precession) sequence with a TR of 50 msec, TE of 15 msec, velocity compensation in the read and section-select directions, acceleration compensation in the read direction, anisotropic volume, and a 1.25-mm partition thickness produced three-dimensional angiographic MR images that were accurate and reproducible in the depiction of the major intracranial vessels. Difficulties with field of view, persistent signal void secondary to higher-order motion, and spatial resolution remain major problems requiring additional study.  相似文献   
10.
The constitutive androstane receptor (CAR; NR1I3) regulates the expression of genes involved in xenobiotic metabolism. Alternative splicing of the human CAR gene yields an array of mRNAs that encode structurally diverse proteins. One form of CAR, termed CAR2, contains an additional four amino acids (SPTV) that are predicted to reshape the ligand-binding pocket. The current studies show a marked, ligand-independent, CAR2-mediated transactivation of reporters containing optimal DR-3, DR-4, and DR-5 response elements, and reporters derived from the natural CYP2B6 and CYP3A4 gene promoters. Overexpression of the RXRalpha ligand binding domain was critical for achieving these effects. CAR2 interaction with SRC-1 was similarly dependent on the coexpression of RXRalpha. Mutagenesis of Ser233 (SPTV) to an alanine residue yielded a receptor possessing higher constitutive activity. Alternatively, mutating Ser233 to an aspartate residue drastically reduced the transactivation capacity of CAR2. The respective abilities of these mutagenized forms of CAR2 to transactivate a DR-4 x 3 reporter element correlated with their ability to interact with RxRalpha and to recruit SRC-1 in a ligand-regulated manner. Together, these results demonstrate a robust RXRalpha-dependent recruitment of coactivators and transactivation by CAR2. In addition, CAR2 displays novel dose responses to clotrimazole and androstanol compared with the reference form of the receptor while at the same time retaining the ability to bind CITCO. This result supports a hypothesis whereby the four-amino-acid insertion in CAR2 structurally modifies its ligand binding pocket, suggesting that CAR2 is regulated by a set of ligands distinct from those governing the activity of reference CAR.  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