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   12236篇
  免费   941篇
  国内免费   4篇
  13181篇
  2022年   84篇
  2021年   196篇
  2020年   136篇
  2019年   182篇
  2018年   193篇
  2017年   185篇
  2016年   315篇
  2015年   449篇
  2014年   589篇
  2013年   711篇
  2012年   863篇
  2011年   903篇
  2010年   554篇
  2009年   547篇
  2008年   702篇
  2007年   722篇
  2006年   699篇
  2005年   635篇
  2004年   615篇
  2003年   599篇
  2002年   581篇
  2001年   147篇
  2000年   98篇
  1999年   127篇
  1998年   132篇
  1997年   112篇
  1996年   105篇
  1995年   117篇
  1994年   84篇
  1993年   116篇
  1992年   86篇
  1991年   60篇
  1990年   74篇
  1989年   62篇
  1988年   53篇
  1987年   61篇
  1986年   47篇
  1985年   66篇
  1984年   91篇
  1983年   65篇
  1982年   94篇
  1981年   82篇
  1980年   66篇
  1979年   48篇
  1978年   49篇
  1977年   41篇
  1976年   35篇
  1975年   37篇
  1974年   63篇
  1973年   36篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.

Background

Student choice is an important determinant of the distribution of specialties of practising physicians in many countries. Understanding characteristics at entry into medical school that are associated with the choice of residency in family medicine can assist medical schools in admitting an appropriate mix of students to serve the health care needs of their regions.

Methods

From 2002 to 2004, we collected data from students in 15 classes at 8 of 16 Canadian medical schools at entry. Surveys included questions on career choice, attitudes to practice and socio-demographic characteristics. We followed students prospectively with these data linked to their residency choice. We used multiple logistic regression analysis to identify entry characteristics that predicted a student’s ultimate career choice in family medicine.

Results

Of 1941 eligible students in the participating classes, 1542 (79.4%) contributed data to the final analyses. The following 11 entry variables predicted whether a student named family medicine as his or her top residency choice: being older, being engaged or in a long-term relationship, not having parents with postgraduate university education nor having family or close friends practicing medicine, having undertaken voluntary work in a developing nation, not volunteering with elderly people, desire for varied scope of practice, a societal orientation, a lower interest in research, desire for short postgraduate training, and lower preference for medical versus social problems.

Interpretation

Demographic and attitudinal characteristics at entry into medical school predicted whether students chose a career in family medicine.The number of physicians per capita in both Canada and the United States has declined, and this decline is expected to continue. Canada has already experienced a drop of 5.1% in the physician-to-population ratio from a peak in 2000, and in the United States a shortage of up to 200 000 physicians, or 20% of the needed workforce, is predicted to occur by 2025.1,2 Combined with a growing elderly population and decreasing physician-hours,3,4 this reduction in the physician-to-population ratio is expected to have implications for the health care systems of both countries. Therefore, health resource planners likely will be looking to expand the role of primary care, and of family medicine in particular.58 To support such an expansion, a commensurate increase in the numbers of domestically trained family physicians will be required. But with as few as 25% (in 2003)9 of Canadian medical graduates choosing family medicine as their top career choice in the residency match, it is unlikely the health care system will be able to supply adequate numbers of primary care physicians.In most countries, the number and the distribution of specialties of physicians are determined by numerous factors, including government policies, training opportunities, immigration and emigration of providers, sex and age distribution of providers, and remuneration incentives and disincentives.1017 In many medical systems, the career interests of students also have a substantial steering effect on the distribution and number of available physicians.18,19The purpose of this study was to follow a large cohort of Canadian medical students from school entry through exit to examine how their career aspirations changed over time and to identify, using multiple logistic regression analysis, the variables at entry into medical school that predict a career choice of family medicine at graduation.  相似文献   
992.

Background:

The foreign-born population bears a disproportionate health burden from tuberculosis, with a rate of active tuberculosis 20 times that of the non-Aboriginal Canadian-born population, and could therefore benefit from tuberculosis screening programs. We reviewed evidence to determine the burden of tuberculosis in immigrant populations, to assess the effectiveness of screening and treatment programs for latent tuberculosis infection, and to identify potential interventions to improve effectiveness.

Methods:

We performed a systematic search for evidence of the burden of tuberculosis in immigrant populations and the benefits and harms, applicability, clinical considerations, and implementation issues of screening and treatment programs for latent tuberculosis infection in the general and immigrant populations. The quality of this evidence was assessed and ranked using the GRADE approach (Grading of Recommendations Assessment, Development and Evaluation).

Results:

Chemoprophylaxis with isoniazid is highly efficacious in decreasing the development of active tuberculosis in people with latent tuberculosis infection who adhere to treatment. Monitoring for hepatotoxicity is required at all ages, but close monitoring is required in those 50 years of age and older. Adherence to screening and treatment for latent tuberculosis infection is poor, but it can be increased if care is delivered in a culturally sensitive manner.

Interpretation:

Immigrant populations have high rates of active tuberculosis that could be decreased by screening for and treating latent tuberculosis infection. Several patient, provider and infrastructure barriers, poor diagnostic tests, and the long treatment course, however, limit effectiveness of current programs. Novel approaches that educate and engage patients, their communities and primary care practitioners might improve the effectiveness of these programs.  相似文献   
993.
Using Toll-like receptor (TLR) and MyD88 gene knock-out (GKO) mice the effect of TLRs and MyD88 on virus replication, interferon (IFN)-β production, natural killer (NK) cell and CD8T cell responses were assessed following ectromelia virus (ECTV) and recombinant vaccinia virus (rVV) infection. The capacity for rVVs encoding cytokines to restore immune function in MyD88(-/-) mice was clearly demonstrated. Results showed that TLR2(-/-), TLR4(-/-)and TLR7(-/-) mice survived ECTV infection whereas MyD88(-/-) and TLR9(-/-)mice, in contrast, were highly susceptible. Next, following infection with rVV, MyD88(-/-) mice elicited reduced serum IFN-β, NK cell and CD8T cell responses compared with wild-type mice, whereas TLR9(-/-) mice showed elevated CD8T cell responses. When MyD88(-/-)mice were infected with rVV co-expressing IFN-β these mice were able to restore IFN-β levels and CD8T cell responses but not NK cell activation. Interestingly, even though rVV co-expressing interleukin (IL)-2 enhanced NK cell activation in MyD88(-/-) mice, this was not associated with an antiviral effect, as observed in normal mice. Surprisingly, co-infection with rVV IL-2/rVV IL-12, but not rVV IL-2/rVV IFN-β, restored the attenuated phenotype of rVV IL-2 in MyD88(-/-) mice indicating that the IL-2/IL-12 combination promotes antiviral responses. Our results clearly show that the CD8T cell defect observed in MyD88(-/-) mice to vaccinia virus infection can be restored by rVV-encoding IFN-β demonstrating the critical role of this cytokine in T cell mediated immunity and illustrates that the model can provide an effective platform for the elucidation of cytokine immunobiology.  相似文献   
994.
Introduction of an O-alkoxyphenyl substituent at the 8-position of the 2-morpholino-4H-chromen-4-one pharmacophore enabled regions of the ATP-binding site of DNA-dependent protein kinase (DNA-PK) to be probed further. Structure-activity relationships have been elucidated for inhibition of DNA-PK and PI3K (p110α), with N-(2-(cyclopropylmethoxy)-4-(2-morpholino-4-oxo-4H-chromen-8-yl)phenyl)-2-morpholinoacetamide 11a being identified as a potent and selective DNA-PK inhibitor (IC50 = 8 nM).  相似文献   
995.
A novel series of spirochromane pan-Akt inhibitors is reported. SAR optimization furnished compounds with improved enzyme potencies and excellent selectivity over the related AGC kinase PKA. Attempted replacement of the phenol hinge binder provided compounds with excellent Akt enzyme and cell activities but greatly diminished selectivity over PKA.  相似文献   
996.
4-Aminobenzothieno[3,2-d]pyrimidines were previously identified in a high throughput screening campaign as LIMK1 inhibitors. Scaffold reversal led to the identification of a series of simple 5,6-substituted 4-aminothieno[2,3-d]pyrimidines with low micromolar inhibition of LIMK1.  相似文献   
997.
998.
Knockdown resistance (kdr) in insects, caused by inherited nucleotide polymorphisms in the voltage-gated sodium channel (VGSC) gene, is a major threat to the efficacy of pyrethroid insecticides. Classic kdr, resulting from an L1014F substitution in the VGSC is now present in numerous pest species. Two other substitutions at the L1014 locus have also been reported, L1014S and L1014H. Here we have used expression of L1014 modified Drosophila para VGSCs in Xenopus oocytes with two-electrode voltage clamp to characterise all three mutations. The mutations L1014F and L1014H caused significant depolarizing shifts in the half activation voltage (V50,act) from −17.3 mV (wild-type) to −13.1 and −13.5 mV respectively, whereas L1014S caused no shift in V50,act but its currents decayed significantly faster than wild-type channels. Treatment of the wild-type channel with deltamethrin (≥1 nM), permethrin (≥30 nM) or DDT (≥1 ??M) resulted in hyperpolarizing shifts in V50,act. Deltamethrin, permethrin and DDT also produced “tail currents” with EC50s of 0.043, 0.40 and 65 ??M and maximum modifications of 837, 325 and 7% respectively. L1014F provided a high level of resistance against all insecticides for both measured parameters. L1014H most effectively combated deltamethrin induced tail currents while L1014S strongly resisted the large DDT induced shifts in V50,act. We conclude that L1014H and L1014S may have arisen through heavy exposure to specific pyrethroids and DDT respectively.  相似文献   
999.
The discovery and structure-activity relationship of a novel series of indole-2-carboxamide antagonists of the cannabinoid CB(1) receptor is disclosed. Compound 26i was found to be a high potency, selective cannabinoid CB(1) antagonist.  相似文献   
1000.
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