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   19182篇
  免费   1085篇
  国内免费   147篇
耳鼻咽喉   221篇
儿科学   505篇
妇产科学   665篇
基础医学   2092篇
口腔科学   535篇
临床医学   1571篇
内科学   3808篇
皮肤病学   385篇
神经病学   902篇
特种医学   733篇
外国民族医学   11篇
外科学   3359篇
综合类   345篇
现状与发展   2篇
一般理论   11篇
预防医学   1651篇
眼科学   547篇
药学   1802篇
中国医学   138篇
肿瘤学   1131篇
  2024年   17篇
  2023年   249篇
  2022年   779篇
  2021年   1121篇
  2020年   609篇
  2019年   762篇
  2018年   1026篇
  2017年   602篇
  2016年   629篇
  2015年   643篇
  2014年   898篇
  2013年   1040篇
  2012年   1527篇
  2011年   1677篇
  2010年   943篇
  2009年   683篇
  2008年   962篇
  2007年   969篇
  2006年   887篇
  2005年   857篇
  2004年   741篇
  2003年   687篇
  2002年   609篇
  2001年   144篇
  2000年   119篇
  1999年   98篇
  1998年   78篇
  1997年   75篇
  1996年   72篇
  1995年   65篇
  1994年   61篇
  1993年   53篇
  1992年   50篇
  1991年   57篇
  1990年   56篇
  1989年   48篇
  1988年   53篇
  1987年   46篇
  1986年   39篇
  1985年   40篇
  1984年   39篇
  1983年   36篇
  1982年   34篇
  1981年   25篇
  1980年   21篇
  1978年   16篇
  1977年   18篇
  1976年   17篇
  1974年   17篇
  1973年   19篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
72.
Bio-based silica, lignocellulose, and activated carbon were simply produced via the recycling of Hassawi rice biomass waste of Al-Ahsa governorate in the eastern Saudi Arabia region using a fast chemical treatment procedure. Rice husk and rice straw wastes were collected, ground, and chemically treated with sodium hydroxide to extract silica/silicate from the dried plant tissues. The liquid extract is then treated with acid solutions in order to precipitate silica/silicate at neutral medium. Lowering the pH of the supernatant to 2 resulted in the precipitation of lignocellulose. Thermal treatment of the biomass residue under N2 gas stream resulted in activated carbon production. Separated products were dried/treated and characterized using several physical examination techniques, such as FT-IR, SEM/EDX, XRD, and Raman spectroscopy in order to study their structure and morphology. Silica and lignocelluloses products were then preliminarily used in the treatment of wastewaters and water-desalination processes.  相似文献   
73.
A study was carried out on 180 sera collected from inhabitants of a seepage flooded village (Begiram) in a Nile Delta governorate in Egypt. The aim of the study was to monitor the prevalence of certain arboviruses; some of them are known to be endemic in Egypt. Sera were screened by ELISA except for the HTN by IF, and the results indicated that WN and SFS exhibited the highest prevalence 45.5% followed by SFN (21%). These 3 viruses are known to be endemic in Egypt. The high prevalence of W.N. and S.F.S viruses in Begiram village in comparison to lower rates detected in sera from nearby Sharkqiya governorate collected almost at the same time may reflect the adverse effect of the environmental change in the flooded village. RNF virus which caused a major epidemic in Egypt in 1977 and continued to be circulating until 1980, its antibodies were detected only in those above 20 years of age with a prevalence rate of 5%. Antibodies against two tick borne viruses viz QRF and CCHF were also detected with low prevalence rate 2.75% and 1.1% respectively; also antibodies to the rodent-borne HTN virus were detected with prevalence rate 1.1%. Antibodies to mosquito borne SIN and BAT viruses were not detected in the tested sera.  相似文献   
74.
This work describes the preparation of an analytical microextraction sorbent using a simple and versatile sol–gel hybrid composite, i.e., aramid oligomers wrapping multi-walled carbon nanotubes (CNTs) covalently bonded to a porous silica network. To overcome the inherent shortcomings of the CNTs'' solubility and dispersion in both organic phases and in the sol–gel solution, the outer surface of the CNTs was initially functionalized with carboxylic acid groups and then reacted with both aramid oligomers and 3-aminopropyl triethoxysilane (APTES). The obtained sorbent was characterized by FT-IR, scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). Using sol–gel chemistry, the functionalized CNTs were coated onto SPME fibers and used in conjunction with GC-MS for the analysis of polycyclic aromatic hydrocarbons (PAHs) in water and soil samples. Excellent repeatability (run-to-run RSD% ∼ 8) and reproducibility (fiber-to-fiber RSD% ∼ 6) were achieved in addition to low LODs (0.10–0.30 ng mL−1) and noticeable recovery%. The present method of sorbent preparation led to enhanced thermal and chemical stabilities, a long sorbent lifetime and good affinity towards PAHs. Moreover, the present sorbent enhanced the extraction capability by more than 30% compared to that of commercially available PDMS counterparts.

This work describes the preparation of an analytical microextraction sorbent using a simple and versatile sol–gel hybrid composite, i.e., aramid oligomers wrapping multi-walled carbon nanotubes (CNTs) covalently bonded to a porous silica network.  相似文献   
75.
Moyamoya disease is an unusual occlusive cerebrovascular condition commonly seen in children, marked by stenosis of the internal carotid artery and circle of Willis, causing, cerebral ischemia. Moyamoya syndrome is a Moyamoya-like arteriopathy with risk factors including autoimmune disorders, thyroid disease, sickle cell disease, or Down syndrome. Trisomy 21 is a genetic disorder consistent with specific physical and behavioral characteristics, with intellectual impairment. We describe a rare case of Moyamoya syndrome manifesting as ischemic stroke in an adult with Down syndrome  相似文献   
76.
A series of statistically‐based models have been developed for predicting the formation of individual trihalomethane (THM) species, ranging from chloroform to bromoform, as a function of various reaction conditions. These equations allow a quantitative assessment of bromide effects on overall THM formation as well as THM speciation.  相似文献   
77.
1背景由马来西亚卫生部和马来西亚国民大学(UKM)联合承担的研究项目,主要研究者是Dr·Syed Mohamed AI Junid,研究中心是吉隆坡总医院(GHKL)儿童研究所、UKM医院儿科病房及乌鲁冷岳区(Hulu Langat)医疗中心,研究时间自2004年1月~2006年6月。研究开始前分别获得了马来西亚卫生部  相似文献   
78.
Primary intracranial germ cell tumors are rare, often affecting children and young patients. Germinomas are the most common type of germ cell tumors. We present the case of a 10-year-old child, who was admitted with decreased visual acuity, asthenia, polyuro-polydipsic syndrome, and gait disorder. His biological assessment showed an hypocortisolemia and diabetes insipidus. Imaging found a bifocal process in the suprasellar and pineal region, suggestive of a bifocal germinoma. Imaging data and the positivity of human chorionic gonadotrophin in the cerebrospinal fluid were in favor of the diagnosis of bifocal germinal tumor confirmed by biopsy. Currently the patient is hospitalized in pediatric oncology department.The diagnosis of germ cell tumors is based on imaging, tumor marker assays, and biopsy. They are treated by radiation therapy alone or in combination with reduction chemotherapy, and surgery for tumor residues. The location of the tumor usually makes surgery difficult.  相似文献   
79.
The present study aimed to design and optimize, a nanoconjugate of gabapentin (GPN)-melittin (MLT) and to evaluate its healing activity in rat diabetic wounds. To explore the wound healing potency of GPN-MLT nanoconjugate, an in vivo study was carried out. Diabetic rats were subjected to excision wounds and received daily topical treatment with conventional formulations of GPN, MLT, GPN-MLT nanoconjugate and a marketed formula. The outcome of the in vivo study showed an expedited wound contraction in GPN-MLT-treated animals. This was confirmed histologically. The nanoconjugate formula exhibited antioxidant activities as evidenced by preventing malondialdehyde (MDA) accumulation and superoxide dismutase (SOD) and glutathione peroxidase (GPx) enzymatic exhaustion. Further, the nanoconjugate showed superior anti-inflammatory activity as it inhibited the expression of interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α). This is in addition to enhancement of proliferation as indicated by increased expression of transforming growth factor-β (TGF- β), vascular endothelial growth factor-A (VEGF-A) and platelet-derived growth factor receptor-β (PDGFRB). Also, nanoconjugate enhanced hydroxyproline concentration and mRNA expression of collagen type 1 alpha 1 (Col 1A1). In conclusion, a GPN-MLT nanoconjugate was optimized with respect to particle size. Analysis of pharmacokinetic attributes showed the mean particle size of optimized nanoconjugate as 156.9 nm. The nanoconjugate exhibited potent wound healing activities in diabetic rats. This, at least partly, involve enhanced antioxidant, anti-inflammatory, proliferative and pro-collagen activities. This may help to develop novel formulae that could accelerate wound healing in diabetes.  相似文献   
80.
Cholangiocarcinomas are a heterogeneous group of highly aggressive cancers that may arise anywhere within the biliary tree. There is a wide geographical variation with regards to its incidence, and risk-factor associations which may include liver fluke infection, primary sclerosing cholangitis, and hepatolithiasis amongst others. These tumours are classified into intrahepatic, perihilar and distal based on their anatomical location. Morphologically, intrahepatic cholangiocarcinomas are further sub-classified into small and large duct variants. Perihilar and distal cholangiocarcinomas are usually mucin-producing tubular adenocarcinomas. Cholangiocarcinomas develop through a multistep carcinogenesis and are preceded by dysplastic and in situ lesions. While clinical characteristics and management of these tumours have been extensively elucidated in literature, their ultra-structure and tumour biology remain relatively unknown. This review focuses on the current knowledge of pathological characteristics, molecular alterations of cholangiocarcinoma, and its precursor lesions (including biliary intraepithelial neoplasia, intraductal papillary neoplasms of the bile duct, intraductal tubulopapillary neoplasms and mucinous cystic neoplasm).  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