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   2299篇
  免费   0篇
  国内免费   1篇
电工技术   3篇
综合类   1篇
化学工业   145篇
金属工艺   3篇
机械仪表   38篇
建筑科学   5篇
能源动力   2篇
轻工业   40篇
水利工程   1篇
无线电   5篇
一般工业技术   28篇
冶金工业   2021篇
自动化技术   8篇
  2019年   2篇
  2013年   5篇
  2012年   4篇
  2011年   5篇
  2010年   6篇
  2009年   12篇
  2008年   7篇
  2007年   5篇
  2006年   7篇
  2005年   8篇
  2004年   4篇
  2003年   9篇
  2002年   9篇
  2001年   7篇
  2000年   15篇
  1999年   75篇
  1998年   602篇
  1997年   355篇
  1996年   223篇
  1995年   140篇
  1994年   99篇
  1993年   125篇
  1992年   22篇
  1991年   21篇
  1990年   21篇
  1989年   18篇
  1988年   24篇
  1987年   15篇
  1986年   18篇
  1985年   22篇
  1984年   5篇
  1983年   14篇
  1982年   9篇
  1981年   27篇
  1980年   32篇
  1979年   12篇
  1978年   12篇
  1977年   72篇
  1976年   165篇
  1975年   5篇
  1974年   5篇
  1973年   12篇
  1972年   2篇
  1971年   6篇
  1970年   3篇
  1968年   7篇
  1967年   4篇
  1966年   7篇
  1965年   7篇
  1955年   3篇
排序方式: 共有2300条查询结果,搜索用时 15 毫秒
1.
OBJECTIVE: To assess how often the aetiology is established in patients with uveitis, what systemic disease are found and what is the contribution of the internist to the diagnostic process. DESIGN: Retrospective study. SETTING: University Hospital Leiden, the Netherlands. METHOD: From January 1987 to April 1992, 342 patients presented with uveitis. All patients underwent a standard ophthalmological examination. Referral to an internist and individualised laboratory screening followed in patients with recurrent, chronic, bilateral or panuveitis. Recorded were: ophthalmological data, results of laboratory screening, results of analysis by the internist, final diagnosis and presence of systemic disease. RESULTS: 149 (44%) patients were examined by the internist, 18 (5.2%) were seen by another specialist. In 169 (49%) patients a specific diagnosis was made. 74 (22%) had a systemic disease, 74 a primary ocular disease. In 28 (8%) a systemic disease was presumed (5% were HLA-B27 positive, 3% had abnormal laboratory results); 5 (1%) patients had endophthalmitis as a complication of a septic process. CONCLUSION: In approximately 1/3 of the patients with uveitis a systemic disease was found. Examination by the internist tailored to the individual patient is essential in the evaluation of uveitis patients.  相似文献   
2.
3.
The labile protons of two 32-base-pair, four-arm models of immobile Holliday junctions have been studied by two-dimensional 1H nuclear magnetic resonance (NMR) spectroscopy. Overlap of resonances in the imino-imino region of two-dimensional nuclear Overhauser enhancement (NOE) spectra necessitates the use of a multi-pathway approach for obtaining sequence-specific assignments wherein all possible NOE connectivities to the labile protons are utilized, including those from the 2H of adenine, 5CH3 of thymine, and 5H of cytosine. Resonance assignments are obtained for all slowly exchanging imino and cytosine amino protons. Base-pairing up to and including the junction point is found in all four arms of both Holliday junctions. Several cross-arm NOE connectivities are identified and can be used to infer the geometry of the helical stacking domains. The two Holliday junctions studied, which differ only by the exchange of two base pairs at the branch point, appear to have opposite arm stacking geometries. These assignments form an important part of the critical background for detailed NMR analysis of Holliday junction structure and dynamics.  相似文献   
4.
We reviewed the cases of sixty-two patients who had had a subcutaneous sarcoma to determine the effect of tumor and treatment-related variables on the rates of survival and local recurrence. Fifty-nine (95 per cent) of the patients had had an operation at another hospital before being referred to us. Twenty-nine (47 per cent) of the sixty-two tumors were high-grade, forty-two (68 per cent) were small (five centimeters or less), and thirty (48 per cent) were malignant fibrous histiocytomas. We followed a treatment strategy that consisted of repeat excision with the goal of obtaining wide margins. Excluding thirteen patients who had had a palpable local recurrence at the time of presentation, twenty (49 per cent) of forty-one patients who had had a marginal excision at another hospital had microscopic residual tumor on repeat excision. At a median of fifty-six months after the repeat excision, fifty (81 per cent) of the sixty-two patients had been continuously disease-free, one had no evidence of disease, eight had died of the disease, and three had died of other causes. The five-year rate of disease-free survival was 85 per cent (fifty-three of sixty-two patients). There were three local recurrences, all in patients who had had a marginal resection. No recurrences were noted in patients who had had a wide local excision of the tumor or of the previous operative field. Multivariate analysis revealed that a large tumor (greater than five centimeters), a marginal excision, and adjuvant radiation therapy were associated with a worse prognosis. Excellent rates of survival for patients who have a subcutaneous sarcoma, including those who have a large or high-grade tumor and those who have residual tumor following a previous operation, can be obtained with carefully planned operative treatment alone. We recommend operative excision or repeat excision with wide margins because of the high prevalence of residual tumor. Size is the most important tumor-related factor, and the operative margin is the most important treatment-related factor. The additional value of adjuvant radiation therapy remains unproved.  相似文献   
5.
OBJECTIVE: Pooled bronchoalveolar lavage fluid (BALF), the return of lavage, contains both bronchial and alveolar material which differ from each other. Artifacts may be created by filtering, centrifuging and washing cells before cytopreparation. This study presents reference values of healthy volunteers for the alveolar sample, ALF, cytopreparation being performed without filtration or centrifugation. METHODS: Eighteen healthy, non-smoking volunteers underwent a standard bronchoalveolar lavage using 10 aliquots of 20 ml of saline. Excluding the return of the first and second aliquots, the rest were pooled and examined cytologically, immunocytochemically and biochemically. The mean, standard deviation, and 95% confidence limits were calculated for the following variables: amount of return, estimated content of epithelial lining fluid (ELF), total and differential cell counts on filter and cytocentrifuge (CCF) preparations, computed cell counts per unit volume of ALF, distribution of lymphocyte subgroups CD3+CD2, CD4, CD8, CD19, CD25 and CD57, and the ratio of CD4 to CD8, the amounts of lymphocytes in the same subgroups per volume of ALF, and the concentrations of total protein, albumin, immunoglobulins A, G and M, hyaluronic acid, eosinophilic cationic protein (ECP), procollagen III aminoterminal propeptide (PCP) and beta 2-microglobulin in ALF and in ELF, as well as the ratios of the concentrations of the solutes in ALF to the same in serum. RESULTS: The 95% confidence limits of means for the most important variables were as follows: estimated ELF content 0.42-0.74%; total cells in ALF 76.6-143.0 x 10(6) l-1; distribution of inflammatory cells on filter and CCF slides: macrophages 74.9-83.6 and 81.4-90.1%, lymphocytes 13.1-22.5 and 8.1-16.4%, and neutrophils 1.0-4.1 and 0.7-2.7%, respectively; distribution of lymphocyte subsets: CD3+CD2 85.6-90.6%, CD4 44.3-53.1%, CD8 26.9-35.8%; concentration of solutes in ALF: total protein 44.8-61.3 mg l-1, albumin 15.4-22.2 mg l-1, IgA 1.8-3.4 mg l-1, IgG 3.1-6.1 mg l-1, IgM 0.05-0.26 mg l-1, hyaluronic acid 8.8-11.1 micrograms l-1, ECP 0.19-0.77 micrograms l-1, PCP 0.005-0.58 micrograms l-1, beta 2-microglobulin 62.2-81.5 micrograms l-1. CONCLUSIONS: Our results show that excluding the bronchial sample from ALF of volunteer subjects and omitting filtering and washing before cytopreparation produces cytologic, immunocytochemical and biochemical reference values with reasonable 95% confidence limits to be used in clinical settings.  相似文献   
6.
7.
Retrospectively 78 patients with uni- or bilateral acute acoustic trauma (AAT) were evaluated to assess the therapeutic effect of hyperbaric oxygenation (HBO). All subjects received saline or dextran (Rheomacodrex) infusions with Ginkgo extracts (Tebonin) and prednisone. Thirty six patients underwent additional hyperbaric oxygenation at a pressure of 2 atmospheres absolute for 60 minutes once daily. Both treatment groups were comparable as far as age, gender, initial hearing loss and prednisone dose are concerned. The delay of therapy onset was 15 hours in both groups and treatment was started within 72 hours in all cases. Control audiometry was performed after 6.5 days, when the HBO group had had 5 exposures to hyperbaric oxygenation. The average hearing gain in the group without HBO was 74.3 dB and in the group treated additionally with HBO 121.3 dB (P < 0.004). It is concluded, that hyperbaric oxygenation significantly improves hearing recovery after AAT. Therefore acute acoustic trauma with significant hearing threshold depression remains an otological emergency. Minimal therapy involving waiting for spontaneous recovery, which is mostly incomplete leaving a residual C5 or C6 and handicapping tinnitus, is not the treatment of choice. Randomized prospective clinical trials with a larger patient series are needed and further experimental studies are required to understand the physiological mechanisms of HBO responsible for the clinical success in AAT.  相似文献   
8.
In order to identify Ca2+ ligands in the putative transmembrane domain 6 of the plasma membrane Ca2+ pump, amino acids Asn879, Met882, Asp883, and Ser887 were singly altered. Asn879, Met882, and Asp883 were chosen because the corresponding amino acids have been proposed as Ca2+ ligands in the sarcoplasmic reticulum Ca2+ pump (Clarke, D. M., Loo, T. W., and MacLennan, D. H. (1990) J. Biol. Chem. 265, 6262-6267). For the alterations, a fully active truncated version of the pump was used, because the interaction of Ca2+ with the pump could be studied without interference from calmodulin binding. The mutants at Asn and Asp did not carry out ATP-supported Ca2+ uptake and formed no acylphosphate from [gamma-32P]ATP, suggesting that, like the corresponding amino acids in the sarcoplasmic reticulum Ca2+ pump, these two are Ca2+ ligands. However, all the mutants at the position of Met882 showed some activity. Indeed, the Met882--> Ile mutant was fully active at a saturating Ca2+ concentration and only the K1/2 for Ca2+ activation was shifted slightly upward. Converting the Met to Thr (which is the corresponding residue in the sarcoplasmic reticulum Ca2+ pump) reduced the activity to 20% of the wild type, further emphasizing the differences between the two Ca2+ pumps. The mutant Ser887--> Ala was expressed in greater amounts than, and had a specific activity about 50% higher than, the wild type, indicating that this serine also could not be a Ca2+ ligand and could not replace the missing Thr at position Met882.  相似文献   
9.
10.
A water-soluble antigenic polysaccharide of high M(r) associated with the lipopolysaccharide has been isolated from phenol-water extraction of cells of Campylobacter coli serotype O:30. The polysaccharide and oligosaccharide degradation products formed on O-dephosphorylation and by periodate oxidation followed by reduction have been investigated by one- and two-dimensional 1H, 13C, and 31P NMR. It is concluded that the antigenic polysaccharide has a teichoic acid-like structure with a poly-Ribitol phosphate, [5-Ribitol-1-P]n, backbone with side chains at O-2 of O-(6-deoxy-beta-D-talo-heptopyranosyl)-(1-->4)-(2-acetylamino-2-deoxy-beta-D- glucopyranosyl) units. The structure is unusual in Gram-negative bacteria and is unique in possessing 6-deoxy-D-talo-heptose as a constituent sugar. Evidence for the relationship of the antigenic polysaccharide to the lipopolysaccharide of low M(r) is discussed.  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