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   1945篇
  免费   5篇
电工技术   4篇
综合类   1篇
化学工业   70篇
金属工艺   5篇
机械仪表   21篇
建筑科学   22篇
矿业工程   1篇
能源动力   8篇
轻工业   91篇
水利工程   7篇
无线电   15篇
一般工业技术   53篇
冶金工业   1606篇
原子能技术   14篇
自动化技术   32篇
  2019年   4篇
  2017年   5篇
  2014年   5篇
  2013年   24篇
  2012年   9篇
  2011年   15篇
  2010年   13篇
  2009年   14篇
  2008年   14篇
  2007年   17篇
  2006年   9篇
  2005年   15篇
  2004年   8篇
  2003年   8篇
  2002年   6篇
  2001年   6篇
  2000年   8篇
  1999年   62篇
  1998年   573篇
  1997年   307篇
  1996年   172篇
  1995年   100篇
  1994年   71篇
  1993年   119篇
  1992年   18篇
  1991年   20篇
  1990年   16篇
  1989年   15篇
  1988年   15篇
  1987年   13篇
  1986年   16篇
  1985年   17篇
  1984年   4篇
  1983年   7篇
  1982年   8篇
  1981年   8篇
  1980年   15篇
  1979年   5篇
  1978年   9篇
  1977年   33篇
  1976年   65篇
  1975年   8篇
  1974年   11篇
  1973年   6篇
  1972年   5篇
  1971年   11篇
  1970年   5篇
  1969年   7篇
  1968年   5篇
  1967年   6篇
排序方式: 共有1950条查询结果,搜索用时 15 毫秒
61.
Native milk fat globule (MFG) size, pH, total fat, protein, and lactose composition in milk from individual cows was examined in autumn and spring 2012 and autumn 2013. Mean MFG diameters ranged between 2.5 and 5.7 µm. Some cows were observed to consistently produce small or large MFG throughout the sampling period, though trends were not consistent across all cows. Small-MFG milk contained more total polar lipids; however, the relative proportion of individual polar lipids did not differ with MFG size, with the exception of phosphatidylcholine, which was greater in small-MFG milk. No significant correlation between MFG size and proximate composition, including calculated fat yield or pH, was found. This work revealed a natural cow-to-cow variation in MFG size exists, which could potentially be exploited to improve the functionality of milk for manufacturing and some products.  相似文献   
62.
Two studies of retail fresh, ripened and semi-hard cheeses made from raw, thermized or pasteurized milk were undertaken in the UK during 2004 and 2005 to determine the microbiological quality of these products. Using microbiological criteria in European Commission Recommendations 2004/24/EC and 2005/175/EC, 2% of both raw, thermized (37/1819 samples) and pasteurized (51/2618 samples) milk cheeses were of unsatisfactory quality. Raw or thermized milk cheeses were of unsatisfactory quality due to levels of Staphylococcus aureus at 10(4)cfu g(-1), Escherichia coli at 10(5)cfu g(-1), and/or Listeria monocytogenes at 10(2)cfu g(-1), whereas pasteurized milk cheeses were of unsatisfactory quality due to S. aureus at 10(3)cfu g(-1) and/or E. coli at 10(3)cfu g(-1). Salmonella was not detected in any samples. Cheeses were of unsatisfactory quality more frequently when sampled from premises rated as having little or no confidence in management and control systems, and stored/displayed at above 8 degrees C. Raw or thermized milk cheeses were also more likely to be of unsatisfactory quality when they were unripened types, and pasteurized milk cheeses when they were: semi-hard types; from specialist cheese shops or delicatessens; cut to order. These results emphasize the need for applying and maintaining good hygiene practices throughout the food chain to prevent contamination and/or bacterial growth. Labelling of cheeses with clear information on whether the cheese was prepared from raw milk also requires improvement.  相似文献   
63.
64.
The use of hydroxyethyl starch (HES) as a cryoprotective agent for human erythrocytes is examined in detail. The molecular properties of the HES pertinent to cryoprotection are described and some conditions for the optimal use of HES in this role are defined. In agreement with the results of other workers, HES is shown to afford a considerable amount of protection to human red blood cells during freezing.  相似文献   
65.
This paper attempts to broaden the analysis of the technology transfer phenomenon by refocusing research attention on the level of performance assessment of technology transfer projects. An holistic evaluation framework based on the considerations of an extended Project Life Cycle model is proposed to overcome some of the shortcomings of conventional approaches to project evaluation. This also reinforces the need for open systems thinking in assessing and managing risk of technology transfer projects. The discussion is based on two case studies which articulate the experiences with two integrated mechanisms of technology transfer used in Algeria from 1965 to 1990: turnkey and “product-in-hand”. The aim is to gain a better understanding of the processes of technology transfer and to contribute to the improvement of associated managerial practices in developing economies.  相似文献   
66.
Lee & Radok introduced a simple method of solving viscoelastic contact problems by replacing the elastic modulus by the viscoelastic creep function, (Lee EH, Radok JRM. Journal of Applied Mechanics 1960;27:438-44) but explained why it fails when the contact area decreases. Ting's discovery (Ting TCT. Journal of Applied Mechanics 1966;35:845-54) of the essential mechanism governing unloading of a contact between a sphere and a viscoelastic half-space is used here to develop a relatively simple method of analysis by superposition of an assembly of viscoelastic “Boussinesq” punch indentations. The new method leads to a more convenient form for the variation of the approach during unloading, and this is evaluated for a three-element solid. The same method, with only minor modifications, is then used to evaluate indentation by a conical indenter.  相似文献   
67.
PURPOSE: To describe the prevalence of sexual difficulties in men and women after marrow transplantation (MT), and to define medical, demographic, sexual, and psychologic predictors of sexual dysfunction 3 years after MT. PATIENTS AND METHODS: Four hundred seven adult MT patients were assessed pretransplantation. Survivors repeated measures of psychologic and sexual functioning at 1 and 3 years posttransplantation. RESULTS: Data were analyzed from 102 event-free 3-year survivors who defined themselves as sexually active. Men and women did not differ in sexual satisfaction pretransplantation. At 1 and 3 years posttransplantation, women reported significantly more sexual dysfunction than men. Eighty percent of women and 29% of men reported at least one sexual problem by 3 years after MT. No pretransplantation variables were significant predictors of 3-year sexual satisfaction for women. For men, pretransplantation variables of older age, poorer psychologic function, not being married, and lower sexual satisfaction predicted sexual dissatisfaction at 3 years (R2=.28; P < .001). Women who were more dissatisfied 3 years after MT did not receive hormone replacement therapy (HRT) at 1 -year posttransplantation and were less satisfied at 1 year, but not pretransplantation (R2=.35; P < .001). CONCLUSION: Sexual problems are significant in the lives of MT survivors, particularly for women. Although HRT before 1 year posttransplantation improves sexual function, it does not ensure sexual quality of life. Intervention for women is needed to apply hormonal, mechanical, and behavioral methods to prevent sexual difficulties as early after transplantation as possible.  相似文献   
68.
Missense mutations in the p53 tumor suppressor occur frequently in human breast cancer and influence both the prognosis and response to chemotherapy. Amino acid 175 (equivalent to murine 172) is the second most common site of missense mutations in p53 in human breast cancer. Over 95% of these mutations are arginine-to-histidine (R-H) substitutions resulting in a gain-of-function, and not merely a dominant-negative phenotype. Transgenic mice expressing a p53 172(R-H) construct targeted to the mammary gland by means of a whey acidic protein (WAP) promoter were characterized as a model system in order to determine the specific effects of this mutation on mammary tumorigenesis. Although transgene expression alone had no apparent effect on normal mammary development, transgenic mice treated with the chemical carcinogen dimethylbenz(a)anthracene developed tumors with much shorter latency than did control littermates and had a greater tumor burden. Tumors arising in transgenic mice did not exhibit either decreased apoptosis or increased cell proliferation relative to tumors arising in nontransgenic littermates, but did display increased genomic instability. Large pleiomorphic nuclei were visible in many tumors from transgenic mice, and DNA flow analysis confirmed the presence of significant aneuploid cell populations. Since these transgenic mice develop very few spontaneous tumors, while accelerating carcinogen-and oncogene-mediated tumorigenesis, this mouse model will, therefore, be useful in the investigation of early events in mammary tumorigenesis. It may also be used as a preclinical model to test newly developed chemotherapeutic strategies.  相似文献   
69.
The role of nitric oxide (NO) in the pathophysiology of gram-positive sepsis is uncertain. In inflammatory conditions, high-output NO production is catalyzed by the enzyme inducible nitric oxide synthase (iNOS). The ability of 2 strains of pneumococci, pneumococcal cell wall preparations, and purified pneumococcal capsule (Pnu-Imune 23) to trigger the production of iNOS protein and NO in RAW 264.7 murine macrophages was tested. Live pneumococci, oxacillin-killed pneumococci, and pneumococcal cell wall preparations stimulated the production of iNOS and NO by RAW 264.7 cells in the presence, but not the absence, of low concentrations of recombinant murine interferon-gamma. In contrast, purified pneumococcal capsule induced little or no iNOS or NO production by these cells. Thus, pneumococci stimulate high-output NO production by murine macrophages. The potential role of NO in the pathogenesis of pneumococcal sepsis deserves further study.  相似文献   
70.
The alcohol-deprivation effect (ADE) was examined under 4-hr operant and 24-hr free-choice alcohol access in the alcohol-preferring (P) rat after deprivation intervals from 2 to 4 weeks. Results indicated that adult male P rats responding for 6 weeks on a concurrent FR-5/FR-1 schedule of reinforcement for alcohol and water, respectively, and then deprived of alcohol for 2 weeks, demonstrated a 40% increase in alcohol responding during the first 60 min of alcohol reinstatement. The alcohol deprivation effect was temporary, however, as responding did not differ from baseline levels on the second day of reinstatement. In a second experiment, weanling male and female P rats received 7 weeks of continuous access to alcohol, beginning at 21 days of age, and were then deprived of alcohol for 4 weeks. On the first day of alcohol reinstatement, P rats exhibited a 40% to 45% increase from baseline alcohol drinking levels, with alcohol intake returning to baseline levels by the 3rd day of reinstatement. Although alcohol intake was higher in females than in males when adjustment was made for body weight, there were no gender differences in the magnitude of the alcohol deprivation effect. Taken together, these results indicate that the ADE is a long-lasting phenomenon that occurs under both operant and continuous access conditions in the P rat, and thus these rats may be useful models for the study of factors involved in relapse of alcohol drinking.  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