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   6847篇
  免费   409篇
  国内免费   27篇
耳鼻咽喉   59篇
儿科学   169篇
妇产科学   95篇
基础医学   1033篇
口腔科学   102篇
临床医学   558篇
内科学   1601篇
皮肤病学   94篇
神经病学   668篇
特种医学   266篇
外国民族医学   1篇
外科学   1128篇
综合类   42篇
一般理论   3篇
预防医学   433篇
眼科学   40篇
药学   464篇
中国医学   4篇
肿瘤学   523篇
  2023年   22篇
  2022年   56篇
  2021年   140篇
  2020年   70篇
  2019年   95篇
  2018年   148篇
  2017年   103篇
  2016年   107篇
  2015年   142篇
  2014年   190篇
  2013年   314篇
  2012年   395篇
  2011年   417篇
  2010年   293篇
  2009年   242篇
  2008年   392篇
  2007年   444篇
  2006年   356篇
  2005年   428篇
  2004年   403篇
  2003年   389篇
  2002年   337篇
  2001年   132篇
  2000年   130篇
  1999年   128篇
  1998年   81篇
  1997年   84篇
  1996年   65篇
  1995年   57篇
  1994年   52篇
  1993年   47篇
  1992年   77篇
  1991年   50篇
  1990年   68篇
  1989年   61篇
  1988年   52篇
  1987年   45篇
  1986年   34篇
  1985年   30篇
  1984年   34篇
  1983年   30篇
  1982年   26篇
  1981年   20篇
  1980年   27篇
  1979年   22篇
  1978年   28篇
  1974年   19篇
  1973年   25篇
  1932年   19篇
  1931年   17篇
排序方式: 共有7283条查询结果,搜索用时 984 毫秒
21.
This study was devoted to tumor differentiation in liver MR T1-weighted imaging with superparamagnetic iron oxide (SPIO). Twenty-one patients with 40 liver lesions were studied at 1.5 T. Before and at least 45 minutes after SPIO administration, turbo-field-echo (TFE) T1-weighted, TFE T1 × T2*-weighted (MXT), and fat-suppressed turbo-spin-echo T2-weighted images were acquired. A quantitative analysis was performed blindly. On TFE T1-weighted images, the signal enhancement was ?33% ± 12 for the liver, ?24% ± 2 for adenomas and focal nodular hyperplasia, +60% ± 33 for the hemangiomas; metastases and cyst enhancement were not significant. After SPIO on TFE T1-weighted images, the hemangioma-to-liver signal ratio (149% ± 18) was definitely higher than the mean metastasis-to-liver signal ratio (90% ± 16). This T1-related differentiation ability lacked dramatically on TFE MXT images and, in one case, was reduced on post-SPIO TFE T1-weighted images by a long imaging delay after SPIO administration (2 hours).  相似文献   
22.
Hypersensitivity reactions occurring during barium studies of the gastrointestinal tract are rare. A case is presented with radiographically demonstrated angioedema in the stomach and small bowel accompanied by allergic rhinitis, which was apparently an allergic response to the barium sulfate suspension. The reaction was documented twice during separate challenges to the barium suspension performed several months apart.  相似文献   
23.
BACKGROUND: Genetic factors other than HLA have been reported to be associated with the outcome of organ transplantations. Because binding of FasL to its receptor Fas could play an important role in tubulitis and in the death of graft tubular epithelial cells during kidney allograft rejection, a gene polymorphism recently identified in position -671 in the promoter of the TNFRSF6 gene coding for Fas was investigated in donors. METHODS: A case-control study was performed within a cohort of non-hyperimmunized adult patients who had received cadaveric kidney transplants based on the occurrence or absence of acute cellular rejection in the first 6 months after renal transplantation. Each recipient from the acute rejection group (n = 35) was matched for age (+/- 5 years) and number of HLA-DR mismatches with two recipients within the non-acute rejection group (n = 70). RESULTS: The TNFRSF6-GG genotype was more frequent in donors in the group without rejection episodes. In contrast, patients who received a kidney from a TNFRSF6-A carrier were more likely to experience acute rejection episodes (relative risk nearly 2.1). CONCLUSION: This study suggests that donor TNFRSF6 polymorphism directly or indirectly influences acute kidney rejection episodes.  相似文献   
24.
Microcystic adnexal carcinoma is a rare cutaneous neoplasm characterized by slow but locally aggressive growth, which normally does not lead to systemic metastasis. Frequent local recurrences are reported, which are most likely due to insufficient operative technique. We present the fourth case of cervical ipsilateral metastatic microcystic adnexal carcinoma in an otherwise healthy woman. The patient presented with a previously diagnosed but not completely resected microcystic adnexal carcinoma in the area of the right posterior scalp and two palpable ipsilateral lymph nodes. The tumor was resected using intraoperative snap frozen histological evaluation of the resection borders. In the same procedure two lymph nodes were resected from the right neck. The lymph nodes were histologically assessed and showed infiltration by small strains of tumor cells. After exclusion of a second primary tumor, e.g., mammary carcinoma, as the cause for cervical lymph node metastases, we performed a modified radical neck dissection with resection of the sternocleidomastoid muscle and the accessory nerve, which was histologically proven to be perineurally infiltrated by tumor cells. In this second procedure the histological evaluation of the specimen showed no sign of remaining tumor infiltration. After exclusion of distant metastasis the patient was irradiated with 60 Gy. The patient is well 1 year after the initial treatment without signs of recurrence.  相似文献   
25.
26.
The pathogenesis of chronic pelvic pain syndrome continues to be an enigma. The observation of inflammatory cells in urine, ejaculate, prostate fluid, and prostate tissue combined with changed local expressions of cytokines, immunoglobulins, complement, and other inflammatory markers led to the hypothesis of an involvement of the immune system in this clinical entity. This review presents a survey of the immunology-related data available for chronic pelvic pain syndrome and attempts to explain them in the context of causes and consequences.  相似文献   
27.
A study is presented in which the authors have examined the effects of pulse configuration, stimulation intensity, and coil current direction during magnetic stimulation. Using figure-8 and circular coils, the median nerve was stimulated at the cubital fossa and at the wrist of 10 healthy volunteers, and the response amplitude and site of stimulation were determined. The key findings of this study are in agreement with other researchers' findings and confirm that biphasic stimulating pulses produce significantly higher M-wave amplitudes than monophasic stimulating pulses for the same stimulus intensity. Mean response amplitudes for biphasic stimuli applied by both coils at the elbow and wrist are consistently higher for the normal current direction. Mean response amplitudes for monophasic pulses are almost always higher for reversed currents. The site for effective stimulation (the position of the virtual cathode) cannot be defined within a fixed distance from the center of the coil (3 to 4 cm), as has been suggested by other researchers, but was found to vary depending on the coil current amplitude and direction as well as the degree of inhomogeneity of the tissues surrounding the nerve. There is a statistically significant relationship between virtual cathode shift and stimulus intensity for biphasic and monophasic pulses. Reversing the coil current direction has no statistically significant effect on the virtual cathode position. Virtual cathode shifts can be measured for biphasic and monophasic stimulations using a figure-8 coil at the wrist and the elbow. However, such a shift is difficult to determine with a circular coil.  相似文献   
28.
An enzyme-linked immunosorbent assay (ELISA) was developed for the quantification of serum antibodies against group-specific epitopes of the glycoproteins (G1, G2) and nucleoprotein (NP) of the genus Hantavirus. This assay was used to study the kinetics of the development of serum antibodies after natural infection with Puumala-like virus in humans. To this end a panel of 34 serum samples collected from individuals at different times after natural infection was tested by the ELISA. The samples were also tested for specific IgM and IgG levels against Puumala-like virus, which provided confirmatory data about the presumed timing of infection. It was shown that serum antibodies against the G1 epitope were present in the acute and early convalescent period just before antibodies to the NP epitope could be demonstrated. In contrast, antibodies to two G2 epitopes were present not earlier than in the convalescent and late convalescent period. Since all these categories of antibodies seem to persist for long periods, antibodies against the G1 epitope and the NP epitope may be of specific diagnostic value. Furthermore, levels of G1-specific antibodies and antibodies to either NP or G2 may allow estimation of the time elapsed following initial infection.  相似文献   
29.
Interleukin (IL)-2 and IL-4 are considered as important regulators of growth and differentiation of lymphocytes. We report that in mice made deficient for both IL-2 and IL-4 by gene targeting all major T cell subsets and B cells were normal, indicating that IL-2 and IL-4 are not essential for development of the immune system. Paradoxically, proliferation of T cells was increased in both IL-2- and IL-4-deficient homozygous mice.  相似文献   
30.
The aim of this study is to improve the dissolution properties of a poorly-soluble active substance, Eflucimibe by associating it with gamma-cyclodextrin. To achieve this objective, a new three-step process based on supercritical fluid technology has been proposed. First, Eflucimibe and cyclodextrin are co-crystallized using an anti-solvent process, dimethylsulfoxide being the solvent and supercritical carbon dioxide being the anti-solvent. Second, the co-crystallized powder is held in a static mode under supercritical conditions for several hours. This is the maturing step. Third, in a final stripping step, supercritical CO(2) is flowed through the matured powder to extract the residual solvent. The coupling of the first two steps brings about a significant synergistic effect to improve the dissolution rate of the drug. The nature of the entity obtained at the end of each step is discussed and some suggestions are made as to what happens in these operations. It is shown the co-crystallization ensures a good dispersion of both compounds and is rather insensitive to the operating parameters tested. The maturing step allows some dissolution-recrystallization to occur thus intensifying the intimate contact between the two compounds. Addition of water is necessary to make maturing effective as this is governed by the transfer properties of the medium. The stripping step allows extraction of the residual solvent but also removes some of the Eflucimibe which is the main drawback of this final stage.  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