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   6448篇
  免费   21篇
电工技术   21篇
化学工业   370篇
金属工艺   5篇
机械仪表   16篇
建筑科学   14篇
矿业工程   2篇
能源动力   13篇
轻工业   533篇
水利工程   3篇
石油天然气   2篇
武器工业   2篇
无线电   92篇
一般工业技术   113篇
冶金工业   5227篇
原子能技术   4篇
自动化技术   52篇
  2016年   11篇
  2013年   87篇
  2012年   12篇
  2011年   19篇
  2010年   26篇
  2009年   25篇
  2008年   18篇
  2007年   25篇
  2006年   21篇
  2005年   20篇
  2004年   18篇
  2003年   20篇
  2001年   13篇
  2000年   15篇
  1999年   145篇
  1998年   1552篇
  1997年   877篇
  1996年   600篇
  1995年   350篇
  1994年   328篇
  1993年   343篇
  1992年   66篇
  1991年   112篇
  1990年   81篇
  1989年   108篇
  1988年   108篇
  1987年   103篇
  1986年   94篇
  1985年   62篇
  1984年   26篇
  1983年   36篇
  1982年   48篇
  1981年   52篇
  1980年   71篇
  1979年   25篇
  1978年   50篇
  1977年   164篇
  1976年   371篇
  1975年   41篇
  1974年   24篇
  1973年   25篇
  1972年   30篇
  1971年   28篇
  1970年   22篇
  1969年   11篇
  1967年   11篇
  1966年   11篇
  1965年   14篇
  1964年   11篇
  1956年   10篇
排序方式: 共有6469条查询结果,搜索用时 187 毫秒
101.
102.
Radical abdominopelvic lymphadenectomy for rectal cancer is based on the tenet that removal of all potentially involved lymphatic tissue will yield a lower rate of locoregional failure and improve survival. At centers with extensive experience with the procedure, the operating time is only modestly prolonged compared with conventional resection. Blood loss and postoperative hospitalization are not significantly increased. Urinary dysfunction and impotence associated with radical abdominopelvic lymphadenectomy (as high as 80 percent and 76 percent, respectively, in recent series) have been major deterrents to its more routine application. Preservation of the hypogastric plexus and even selective preservation of a unilateral S4 nerve root have been shown to reduce the occurrence of genitourinary complications. Improved five-year survival of 68 percent and local recurrence rates of 5 to 20 percent for TNM Stage III cancers have been achieved with radical abdominopelvic lymphadenectomy. These results compare favorably with recent trials of adjuvant chemoradiation after conventional resection in stage-matched patients. The rationale, evolution, and application of radical abdominopelvic lymphadenectomy to the surgical management of rectal cancer are critically examined. The potential benefits of radical abdominopelvic lymphadenectomy, which have been demonstrated in nonrandomized trials, should be evaluated in a prospective and properly randomized study to clearly establish or refute its efficacy.  相似文献   
103.
The IgE-mediated allergic response involves a series of physiological pathways that result in the array of symptoms commonly associated with allergy. This article describes the mediators that prompt specific clinical responses and identifies those at risk for latex hypersensitivity.  相似文献   
104.
Eighteen multiparous Holstein cows in midlactation were used in a switchback design trial to evaluate the effect of chop length (3 or 30 mm) of timothy grass silage, containing less than 30% ADF and treated with formic acid, on DMI and cow performance. Within chop length, addition of NaHCO3 (2% of DMI) or the replacement of 30% of silage DM with juice-extracted grass pellets was also evaluated. Cows were fed a TMR composed of 90% silage and 10% concentrate. Silage preservation characteristics were not different between chop lengths. The DMI and apparent digestibility were similar among treatments. Yields of 4% FCM (24.9 vs. 22.7 kg/d), fat (1.03 vs. .93 kg/d), and protein (.83 vs .77 kg/d) were higher with the short chopped silage. Milk protein, milk NPN content, and serum urea were higher for cows fed long chopped silage. Yields of milk and milk constituents were not affected by the addition of juice-extracted grass pellets or NaHCO3. Fat percentage and fatty acid composition of milk remained unchanged by treatments. Reduction of particle size, from 30 to 3 mm, of timothy grass, treated with formic acid at harvest and using compaction at ensiling in bag silos, did not affect silage conservation characteristics but did improve milk, fat, and protein yields when cows were fed high silage diets.  相似文献   
105.
PURPOSE: To assess the non-cutaneous involvement in primary B-cell non-Hodgkin's lymphoma (NHL) of the skin. PATIENTS AND METHODS: Data from 45 patients with B-cell NHL of the skin were retrospectively analysed. The patients were diagnosed on histologic and immunocytochemical grounds between June 1977 and July 1993, and 14 cases were selected for their exclusively cutaneous initial involvement. Initial treatment, response to therapy, disease-free survival characteristics of relapse and therapeutic sequence were evaluated in every case. RESULTS: Cutaneous involvement presented as nodules or patches, on a single location, in 12 cases, or disseminated, in 2 others. No prognostic factor could be identified, and complete remission was attained in all cases. Cutaneous relapse was seen in 7 patients after 4 to 108 months since diagnosis. Extracutaneous dissemination was not seen in any case, and 13 patients are alive and disease-free. A 90 year-old woman died of toxic complications. CONCLUSIONS: The clinical facts reported here confirm the not too aggressive behaviour of certain B-cell cutaneous NHL, probably related with their origin on the skin itself.  相似文献   
106.
107.
A prospective assessment of late changes in breast appearance in 559 patients after tumour excision and radiotherapy for early breast cancer noted a strong association with breast size. Only 3/48 (6%) patients with small breasts developed moderate or severe late changes compared with 94/423 (22%) with medium sized breasts and 34/88 (39%) patients with large breasts (p < 0.001). One possibility is that greater radiation changes are related to greater dose inhomogeneity in women with large breasts. To explore this hypothesis, radiation dose distributions were assessed in a separate group of 37 women in whom three-level transverse computer tomographic images of the breast in the treatment position were available. A significant correlation was found between breast size and dose inhomogeneity which may account for the marked changes in breast appearance reported in women with large breasts.  相似文献   
108.
109.
OBJECTIVE: The pathogenesis of neurologic and neuropsychologic dysfunction in HIV-1 infection is unclear. The purpose of the study was to determine an association between cerebral perfusion and HIV-1-related ocular microangiopathic syndrome. METHODS: We studied 28 HIV-1-infected patients, seven of whom presented with asymptomatic HIV infection, nine with lymphadenopathy syndrome or AIDS-related complex, and 12 with AIDS. Cerebral perfusion was semi-quantitatively measured by single photon emission computed tomography of the brain using technetium-99 hexamethyl-propylenamine oxime (HMPAO-SPECT). The conjunctival manifestation of HIV-1-related microangiopathic syndrome was measured by a rating scale determining blood-flow sludging and, retinal cotton-wool spots were counted. CD4 count, neopterin, beta 2-microglobulin (beta 2M), haemoglobin, and age were determined as putative confounding variables. RESULTS: Mean conjunctival sludge in patients with normal HMPAO-SPECT findings was 1.3 +/- 0.5 (mean +/- s.e.m.); no cotton-wool spots were present. In patients with slightly impaired HMPAO-SPECT, it was 2.1 +/- 0.6 and mean cotton-wool spot count was 1.1 +/- 0.4. In patients with severely impaired HMPAO-SPECT, mean conjunctival sludge was 4.5 +/- 0.3 and mean cotton-wool spot count was 4.9 +/- 1.1 HMPAO-SPECT findings were closely associated with conjunctival sludge (r = 0.72; P < 0.001) and number of cotton-wool spots (r = 0.78; P < 0.001), whereas only a slight association with staging of HIV disease was found (P = 0.052). Analysis of covariance controlling for CD4 count neopterin, beta 2M, age, and haemoglobin demonstrated a significant difference between the three HMPAO-SPECT groups for both the number of cotton-wool spots (P < 0.001) and the conjunctival sludge rating (P < 0.001). CONCLUSION: There was a close association between severity of HIV-1-related ocular microangiopathic syndrome and severity of cerebral hypoperfusion. Microvascular alterations might contribute to the pathogenesis of neurological and neuropsychological symptoms in patients with HIV-1 disease. Furthermore, the conjunctival sludge rating and the number of cotton-wool spots might be appropriate indicators for severity of microvascular changes of the central nervous system [corrected].  相似文献   
110.
In situ FTIR spectroscopy has been applied to study the reason of the different selectivity behaviour of rhodium in the CO hydrogenation reaction in dependence on the different particle size. Several forms of molecularly adsorbed CO are observed, such as linearly- and bridgedbonded CO on metallic rhodium as well as dicarbonyl species with Rh(I) centres formed by oxidation of Rh(0) with protons in presence of CO. Furthermore, non-reactive formate, acetate, and carbonate species are produced as side products of the reaction. The higher selectivity to oxygenates, particularly to methanol, is explained by the existence of multiple-bonded CO present only on small rhodium crystallites. The multiple-bonded CO formed at low temperatures is converted at higher temperatures to the highly reactive formyl species, which is hydrogenated to methanol.  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