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   6010篇
  免费   422篇
  国内免费   21篇
耳鼻咽喉   48篇
儿科学   210篇
妇产科学   166篇
基础医学   934篇
口腔科学   93篇
临床医学   544篇
内科学   1108篇
皮肤病学   105篇
神经病学   513篇
特种医学   97篇
外科学   628篇
综合类   135篇
一般理论   7篇
预防医学   501篇
眼科学   204篇
药学   600篇
中国医学   76篇
肿瘤学   484篇
  2023年   58篇
  2022年   134篇
  2021年   181篇
  2020年   114篇
  2019年   146篇
  2018年   186篇
  2017年   117篇
  2016年   145篇
  2015年   173篇
  2014年   227篇
  2013年   316篇
  2012年   451篇
  2011年   463篇
  2010年   277篇
  2009年   225篇
  2008年   352篇
  2007年   329篇
  2006年   342篇
  2005年   302篇
  2004年   258篇
  2003年   217篇
  2002年   204篇
  2001年   109篇
  2000年   103篇
  1999年   69篇
  1998年   57篇
  1997年   46篇
  1996年   22篇
  1995年   24篇
  1994年   27篇
  1993年   23篇
  1992年   55篇
  1991年   55篇
  1990年   47篇
  1989年   55篇
  1988年   40篇
  1987年   34篇
  1986年   30篇
  1985年   36篇
  1984年   27篇
  1983年   32篇
  1982年   20篇
  1981年   17篇
  1980年   18篇
  1979年   35篇
  1978年   18篇
  1977年   23篇
  1974年   19篇
  1973年   17篇
  1972年   17篇
排序方式: 共有6453条查询结果,搜索用时 0 毫秒
71.
Background Second targeted therapies for metastatic renal cell carcinoma (mRCC) include mammalian target of rapamycin inhibitors (mTORis) and tyrosine kinase inhibitors (TKIs). This observational study compares overall survival (OS) and progression-free survival (PFS) of patients treated with everolimus (an mTORi) and axitinib (a TKI) following first TKI, and assesses the impact of type and duration of first TKI on the relative effectiveness of these second targeted therapies.

Methods Retrospective reviews of medical records were conducted by medical oncologists or hematologists/oncologists recruited from a nationwide panel. Included patients with mRCC were required to have discontinued a first TKI (sunitinib, sorafenib, or pazopanib) for medical reasons, and to have initiated everolimus or axitinib as second targeted therapy between February 2012 and January 2013. OS and PFS were compared between patients treated with everolimus vs. axitinib using multivariable Cox proportional hazards regression models. Comparative results were also stratified by type and duration of first TKI.

Results Included patients (n?=?325 for everolimus and n?=?127 for axitinib) had a mean age of 61 years and 31% were female. Sunitinib was the most commonly used first TKI (73%). After adjusting for patient characteristics, no statistically significant differences were observed in OS or PFS between everolimus and axitinib. When stratifying by type and duration of first TKI, there was no statistically significant difference in OS between everolimus and axitinib in all subgroups except for patients with?<6 months on sunitinib or sorafenib as first TKI. No significant difference in PFS was observed in any subgroup.

Limitations Important limitations include potential missing or inaccurate data in medical charts, and confounding due to unobserved factors.

Conclusions In this retrospective chart review, no significant differences were detected in OS or PFS between axitinib and everolimus as second targeted therapy. Longer duration of first TKI was not associated with increased effectiveness of subsequent axitinib compared to everolimus.  相似文献   
72.
73.
STUDY OBJECTIVE: To evaluate regression rates among adolescents (aged < or =21) with cervical intraepithelial neoplasia (CIN) 2 managed expectantly and to determine factors associated with disease regression. DESIGN: Cohort study using a colposcopic database of 2,996 women seen between August 1999 and November 2005. SETTING: Colposcopy clinic in urban, tertiary care medical center. PARTICIPANTS: Adolescents with CIN 2. Routine management consisted of two options: immediate treatment or repeat colposcopic evaluation in 6 months. MAIN OUTCOME MEASURES: For those managed conservatively, regression was defined either as a subsequent normal colposcopy and/or biopsy and at least 2 smears read as negative for epithelial abnormality or at least 3 consecutive negative smears if repeat colposcopy was not performed. Demographic information, including age, was assessed to determine possible associations with disease regression. RESULTS: Of the 93 adolescents, 53 (57%) elected to undergo immediate treatment with a diagnostic excisional procedure, and 40 (43%) chose management with colposcopic follow-up. Of those treated, high-grade disease (CIN 2+) was found in 40 (75%). Of the 36 young women followed conservatively (4 were lost to follow-up), regression after a median follow-up time of 378 days was documented in 14 (39%). Of the 22 adolescents not fulfilling our criteria for regression, only 3 had evidence of CIN 2 or worse during follow-up. The remaining 19 had either CIN 1 or mildly abnormal cytologic results. Kaplan-Meier survival estimates indicated younger age (< or =16 years) tended to be associated with decreased time to regression. CONCLUSION: Based on significant regression of CIN 2 among adolescent women, primary management in this population should consist of cytologic and colposcopic follow-up.  相似文献   
74.
1. Smears from the nasal cavities of fifteen patients suffering from kala-azar have been examined and in nine of these typical Leishman-Donovan bodies have been found. 2. Smears from the surface of the tonsil and from the saliva in one of the above nine cases showed the presence of leishmania. The tonsils of this patient, who died as the result of kala-azar and secondary infection, at autopsy were shown to be massively infected with Leishman-Donovan bodies. 3. Leishmania in the nasal discharge of two patients were shown by inoculation into susceptible animals to be viable and capable of producing infection. Sufficient time has not elapsed to determine the viability of the organisms from the remaining cases. 4. These experiments show for the first time that a rich source of infective material from a large proportion of patients with kala-azar is available for direct transmission of the disease. 5. Strong evidence is presented as a basis for the concept that one of the natural modes, perhaps the most important natural mode, of transmission of kala-azar is from person to person by way of the upper respiratory and alimentary tracts. 6. Two normal human volunteers and numerous normal experimental animals have been inoculated into the nasal and oral cavities with the nasal discharge, known to contain leishmania, from patients with kala-azar. The results of these experiments will be reported at a subsequent date.  相似文献   
75.
A 73-year-old lady presented with a white spot and redness in the left eye for 1 month and had been treated elsewhere as a case of fungal keratitis. She had severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) viral infection 2 months before. Her past ocular history and examination gave a probable diagnosis of herpetic stromal and endothelial keratitis. She responded to oral acyclovir and topical steroid, leading to resolution of stromal edema and inflammation. Anterior chamber fluid polymerase chain reaction (PCR) confirmed pathogen herpes simplex virus (HSV)-1. HSV ocular reactivation after coronavirus disease 2019 (COVID-19) has been reported currently. The present report will add knowledge about this potential opportunistic ophthalmic infection during the recovery phase of COVID-19 disease.  相似文献   
76.
Acetaldehyde (CH3CHO) is ubiquitous in interstellar space and is important for astrochemistry as it can contribute to the formation of amino acids through reaction with nitrogen containing chemical species. Quantum chemical and reaction kinetics studies are reported for acetaldehyde formation from the chemical reaction of C(3P) with a methanol molecule adsorbed at the eighth position of a cubic water cluster. We present extensive quantum chemical calculations for total spin S = 1 and S = 0. The UωB97XD/6-311++G(2d,p) model chemistry is employed to optimize the structures, compute minimum energy paths and zero-point vibrational energies of all reaction steps. For the optimized structures, the calculated energies are refined by CCSD(T) single point computations. We identify four transition states on the triplet potential energy surface (PES), and one on the singlet PES. The reaction mechanism involves the intermediate formation of CH3OCH adsorbed on the ice cluster. The rate limiting step for forming acetaldehyde is the C–O bond breaking in CH3OCH to form adsorbed CH3 and HCO. We find two positions on the reaction path where spin crossing may be possible such that acetaldehyde can form in its singlet spin state. Using variational transition-state theory with multidimensional tunnelling we provide thermal rate constants for the energetically rate limiting step for both spin states and discuss two routes to acetaldehyde formation. As expected, quantum effects are important at low temperatures.

Acetaldehyde (CH3CHO) is ubiquitous in interstellar space and is important for astrochemistry as it can contribute to the formation of amino acids. The reaction mechanism for its formation on a methanol ice grain may involve intersystem spin crossing.  相似文献   
77.
In mouse, oral administration of the benzene extract of Hibiscus rosa-sinensis flowers at a dose level of 1 gm/kg body weight/day from day 5-8 of gestation led to termination of pregnancy in about 92% of the animals. The effect was associated with a significant fall in peripheral level of progesterone and increase in uterine acid phosphatase activity, as measured on day 10. The ovary exhibited signs of luteolysis, and the corpus luteal delta 5-3 beta -hydroxysteroid dehydrogenase activity decreased markedly. The interceptive effect of the extract was prevented completely by exogenous progesterone (1 mg/mouse/day) or chorionic gonadotropin (1 I.U./mouse/day) and partially (62.5%) by exogenous prolactin (500 micrograms/mouse/day). In unilaterally pregnant mouse having trauma-induced deciduomata in the sterile horn, the extract caused resorption of the fetuses, and regression of the deciduomata accompanied by reduction in weight of the ovaries. Luteolysis, may be due to interference with the luteotropic influence, and a consequent fall in plasma level of progesterone have been suggested as the plausible cause of termination of pregnancy.  相似文献   
78.
79.
80.
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