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   36510篇
  免费   1853篇
  国内免费   34篇
电工技术   262篇
综合类   20篇
化学工业   7714篇
金属工艺   720篇
机械仪表   789篇
建筑科学   1042篇
矿业工程   78篇
能源动力   659篇
轻工业   5732篇
水利工程   334篇
石油天然气   138篇
武器工业   5篇
无线电   1349篇
一般工业技术   6207篇
冶金工业   8236篇
原子能技术   162篇
自动化技术   4950篇
  2024年   81篇
  2023年   320篇
  2022年   436篇
  2021年   907篇
  2020年   732篇
  2019年   822篇
  2018年   1423篇
  2017年   1378篇
  2016年   1464篇
  2015年   1108篇
  2014年   1424篇
  2013年   2794篇
  2012年   2079篇
  2011年   1963篇
  2010年   1572篇
  2009年   1434篇
  2008年   1379篇
  2007年   1295篇
  2006年   895篇
  2005年   755篇
  2004年   725篇
  2003年   636篇
  2002年   605篇
  2001年   454篇
  2000年   447篇
  1999年   478篇
  1998年   2459篇
  1997年   1709篇
  1996年   1087篇
  1995年   654篇
  1994年   507篇
  1993年   596篇
  1992年   224篇
  1991年   225篇
  1990年   167篇
  1989年   179篇
  1988年   170篇
  1987年   150篇
  1986年   140篇
  1985年   168篇
  1984年   138篇
  1983年   115篇
  1982年   155篇
  1981年   162篇
  1980年   173篇
  1979年   96篇
  1978年   92篇
  1977年   303篇
  1976年   661篇
  1973年   79篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
82.
The authors suggest that academic institutions build business-oriented policies and practices into the development of any nurse-run clinic to set the stage for financial independence when special or development funding ends. One university-affiliated program that provides 4,000 to 5,000 annual visits drastically changed its strategies when threatened with closure after free rent and other subsidies were withdrawn. The growing emphasis on ambulatory care roles for nurses at all levels makes such clinics critical to the success of the broad-based curricula of nursing education programs, as well as the clinic's value to communities they serve. Funding difficulties frequently threaten the existence of such nurse-run clinics once the initial grant funding is no longer available. This has caused a new emphasis on running such clinics in a business-wise manner. Among the strategies initiated were: direct full-pay at the time of service; a realistic business management plan; aggressive planned marketing; contracts and agreements with other agencies; obtaining provider status with selected HMOs.  相似文献   
83.
In addition to receptor-type pinealocytes, the mammalian pineal organ contains small and large neurons and ependymal/glial cells as well. Axons of pinealocytes form synaptic ribbon-containing axo-dendritic synapses on large secondary pineal neurons and/or terminate as neurohormonal endings on the basal lamina of the vascular surface of the organ. The small pineal neurons were found to be gamma-aminobutyric acid (GABA)-immunoreactive, while large secondary neurons and pinealocytes contained immunoreactive amino acids (glutamate and aspartate). Glutamate accumulated presynaptically in pinealocytic axon terminals on large secondary neurons and in the axons of these neurons. Glutamate immunoreactive axons of pineal neurons were traced via the pineal tract to the habenular nucleus. Axons containing granular vesicles and coming from extrapineal perikarya are glutamate immunoreactive as well. Aspartate and GABA are also present in some of the myelinated axons, supposedly pinealopetal in the pineal tract.  相似文献   
84.
BACKGROUND: Locally advanced thyroid cancer invading the tracheal cartilage represents a difficult treatment dilemma during thyroidectomy. METHODS: A retrospective chart review was performed to determine the results of laryngotracheal resection or tracheal cartilage shave with adjuvant radiotherapy in patients with locally advanced thyroid cancer invading the upper airway. RESULTS: Of 597 patients undergoing thyroidectomy for thyroid cancer, 40 were found to have laryngotracheal invasion. Thirty-five patients with superficial invasion underwent cartilage shave procedures with adjuvant radiotherapy; five with full-thickness invasion underwent radical resection, including tracheal sleeve resection (n = 3) or total laryngectomy (n = 2). Histologic subtypes included papillary (n = 32), follicular (n = 2), Hurthle cell (n = 1), medullary (n = 3), and anaplastic (n = 2). Of the cartilage shave group, 25 are currently alive with no evidence of disease at a mean follow-up of 81 months (range 1-290). Six developed isolated local/regional recurrence and were managed with total laryngectomy (n = 1), tracheal resection (n = 1), cervical lymphadenectomy (n = 1), or repeat radiotherapy (n = 3). All six patients remain free of disease at a mean follow-up of 5 years. Of those who underwent initial laryngotracheal resection, four remain free of disease at a mean follow-up of 5 years. The rates of 10-year disease-free survival and overall survival for all patients were 47.9% (95% confidence interval [CI] 24.8, 71.0) and 83.9% (95% CI 70.3, 97.5), respectively. CONCLUSIONS: These data suggest that adequate management of thyroid cancer with laryngotracheal invasion can be achieved with a more conservative surgical approach and adjuvant radiotherapy, reserving more radical resections for extensive primary lesions or locally recurrent disease.  相似文献   
85.
Minimal inhibition concentrations (MIC) of gentamycin (Ge), neomycin (Neo), rifampicin (Rif), ampicillin (Amp), lincomycin (Lin), erythromycin (Ery), and streptomycin (STM) were determined by the agar dilution technique using 46, 130, 131, 125, 140, 139 and 142 strains of Staphylococcus aureus, respectively. The strains, selected from the collection of the authors' laboratory, were isolated from mammary gland secretions of cows affected with clinical or subclinical mastitis. The following ranges of MIC (micrograms/ml) were assessed for the antibiotics under study: Ge 0.125-0.50, Neo 0.06-0.50, Rif 0.0039-0.030, Amp 0.015-1.00, Lin 0.25-1.00, Ery 0.06-0.25, STM 0.50-64.0. Modal MIC (micrograms/ml) were as follows; Ery 0.125 (86%), Lin 0.5 (71.4%), Rif 0.007 (68.7%), Ge 0.25 (56.5%), STM 1.00 (54.2%), Neo 0.25 (53.8%), Amp 0.06 (41.6%). The order of efficiency expressed in MIC 90 (micrograms/ml) was as follows: Rif (0.015), Ery (0.125), Ge (0.25), Neo (0.25), Amp (0.5), STM (4.0).  相似文献   
86.
87.
88.
A novel assay based on a nested PCR and restriction enzyme analysis of the PCR products was developed for the rapid detection and identification of Mycobacterium bovis and M. avium-M. intracellulare species in formalin-fixed, paraffin-embedded tissue (PET) specimens. On the basis of the nucleotide sequence data obtained in the present study, general nested primers were constructed to amplify a 424-bp segment of the gene encoding the 65-kDa surface antigen of mycobacteria. The nested PCR assay proved to be highly sensitive, since as little as 5 to 10 fg of extracted mycobacterial DNA was detected. The safety of the assay as a routine method for the diagnosis of M. bovis and M. avium-M. intracellulare in PET specimens was provided by taking various precautions. In order to prevent false positivity, specific tools and procedures were applied. To detect false-negative results and assess the efficiency of the PCR, an internal standard molecule of amplification was constructed. The digestion of the amplicons with the restriction endonuclease Sau96-I allowed the identification of M. bovis and M. avium-M. intracellulare in a large number of clinical specimens. The present results indicate that PCR combined with an internal control of amplification and restriction enzyme analysis of the amplicons provides a rapid, sensitive, and reliable method for routine diagnostic laboratories to detect and identify M. bovis and M. avium-M. intracellulare in PET specimens.  相似文献   
89.
We have studied the GABAergic projections to the inferior colliculus (IC) of the rat by combining the retrograde transport of horseradish peroxidase (HRP) and immunohistochemistry for gamma-amino butyric acid (GABA). Medium-sized (0.06-0.14 microliter) HRP injections were made in the ventral part of the central nucleus (CNIC), in the dorsal part of the CNIC, in the dorsal cortex (DCIC), and in the external cortex (ECIC) of the IC. Single HRP-labeled and double (HRP-GABA)-labeled neurons were systematically counted in all brainstem auditory nuclei. Our results revealed that the IC receives GABAergic afferent connections from ipsi- and contralateral brainstem auditory nuclei. Most of the contralateral GABAergic input originates in the IC and the dorsal nucleus of the lateral lemniscus (DNLL). The dorsal region of the IC (DCIC and dorsal part of the CNIC) receives connections mostly from its homonimous contralateral region, and the ventral region from the contralateral DNLL. The commissural GABAergic projections originate in a morphologically heterogeneous neuronal population that includes small to medium-sized round and fusiform neurons as well as large and giant neurons. Quantitatively, the ipsilateral ventral nucleus of the lateral lemniscus is the most important source of GABAergic input to the CNIC. In the superior olivary complex, a smaller number of neurons, which lie mainly in the periolivary nuclei, display double labeling. In the contralateral cochlear nuclei, only a few of the retrogradely labeled neurons were GABA immunoreactive. These findings give us more information about the role of GABA in the auditory system, indicating that inhibitory inputs from different ipsi- and contralateral, mono- and binaural auditory brainstem centers converge in the IC.  相似文献   
90.
BACKGROUND: The treatment of severe enterococcus infections requires synergism of a beta-lactamic or glycopeptide and a aminoglycoside, but when resistance to first one or high-level resistance to aminoglycosides are present, synergism would be lost. We compared the adequacy of two commercially available systems to detect antibiotic resistance. METHODS: We studied 158 isolates of Enterococcus sp., with high-level resistance to gentamicin (40 isolates) and streptomycin (89 isolates), resistance to ciprofloxacin (34 isolates), resistance to ampicillin (7 isolates) and with intermediate susceptibility to vancomycin (3 isolates). No one was beta-lactamase producer by Cefinase disk method. We use disk diffusion as reference technique to detect high-level streptomycin resistance. The susceptibility to the remainder antibiotics was studied by agar dilution method, according to NCCLS. We studied the accuracy of GPS-TA cards and Uniscept MIC-3 in relation to the degree of agreement with conventional means, following FDA criteria. RESULTS: Essential agreement for MIC was less than 90 with MIC-3 for ampicillin (81.5%) and ciprofloxacin (71.3%). Categorical agreement rate was less than 90% (76.4%) and major error rate was higher than 3% (10.9%) with the use of MIC-3 for ciprofloxacin. Very major errors for ampicillin, vancomycin and ciprofloxacin were not produced by any system. The very major error rates for high level resistance to gentamicin and streptomycin with GPS-TA card were 5 and 15.7%, respectively. CONCLUSIONS: We do not recommend the use of the Uniscept MIC-3 panel with visual reading to detect susceptibility to ciprofloxacin. Detection of high levels of aminoglucoside resistance by GPS-TA card should be supplemented with conventional techniques because of the high rate of major error. Due to the low number of strains that have been studied, we can not assure the suitability of these systems to detect ampicillin or vancomycin resistance.  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