全文获取类型
收费全文 | 3767篇 |
免费 | 28篇 |
专业分类
电工技术 | 22篇 |
化学工业 | 141篇 |
金属工艺 | 14篇 |
机械仪表 | 19篇 |
建筑科学 | 53篇 |
矿业工程 | 2篇 |
能源动力 | 18篇 |
轻工业 | 91篇 |
水利工程 | 4篇 |
无线电 | 198篇 |
一般工业技术 | 207篇 |
冶金工业 | 2879篇 |
原子能技术 | 14篇 |
自动化技术 | 133篇 |
出版年
2021年 | 12篇 |
2020年 | 12篇 |
2019年 | 9篇 |
2018年 | 16篇 |
2017年 | 9篇 |
2016年 | 11篇 |
2015年 | 8篇 |
2014年 | 23篇 |
2013年 | 38篇 |
2012年 | 27篇 |
2011年 | 39篇 |
2010年 | 36篇 |
2009年 | 47篇 |
2008年 | 38篇 |
2007年 | 39篇 |
2006年 | 40篇 |
2005年 | 26篇 |
2004年 | 29篇 |
2003年 | 36篇 |
2002年 | 27篇 |
2001年 | 28篇 |
2000年 | 21篇 |
1999年 | 110篇 |
1998年 | 896篇 |
1997年 | 457篇 |
1996年 | 286篇 |
1995年 | 207篇 |
1994年 | 190篇 |
1993年 | 193篇 |
1992年 | 48篇 |
1991年 | 45篇 |
1990年 | 35篇 |
1989年 | 50篇 |
1988年 | 40篇 |
1987年 | 49篇 |
1986年 | 48篇 |
1985年 | 53篇 |
1984年 | 22篇 |
1983年 | 22篇 |
1982年 | 27篇 |
1981年 | 31篇 |
1980年 | 42篇 |
1979年 | 22篇 |
1978年 | 15篇 |
1977年 | 66篇 |
1976年 | 159篇 |
1975年 | 19篇 |
1974年 | 12篇 |
1973年 | 10篇 |
1971年 | 11篇 |
排序方式: 共有3795条查询结果,搜索用时 31 毫秒
91.
The effects of linoleic, linolenic and columbinic acids fed as 4% of a high carbohydrate (50% glucose) diet on the activities
and the amounts of several enzymes associated with fatty acid synthesis in livers and mammary glands of lactating mice were
compared with those for stearic and oleic acids. Fatty acid synthesis, measured in vivo, was significantly lower in livers
of mice ingesting all 3 polyunsaturated fatty acids (PUFA), whereas in mammary glands synthesis was lower only in mice receiving
columbinic acid. The activities of fatty acid synthetase (FAS) and acetyl CoA carboxylase were significantly reduced in liver
by all 3 PUFA, as were activities of glucose-6-phosphate dehydrogenase, malic enzyme (ME) and citrate cleavage enzyme (CCE),
also associated with lipogenesis. In mammary gland, on the other hand, the activities of these enzymes were unaffected by
dietary PUFA. The tissue contents of FAS, ME and CCE, measured by rocket immunoelectrophoresis, were found to be significantly
reduced in liver by linoleate, linolenate and columbinate but were not significantly altered in mammary gland. The decrease
in hepatic lipogenesis observed was principally due to a decrease in the amounts of these enzymes induced by the dietary PUFA
but the inhibition in mammary gland caused by columbinate could not be accounted for by a reduction in enzyme contents and
therefore may be due to allosteric effects which occur when fatty acid synthesis is measured with3H2O. The fatty acid composition in liver and mammary gland of dams and in liver and kidney of pups completely reflected dietary
fatty acids. Columbinate made up ca. 20% of the total fatty acids in both tissues of the columbinic acid-fed mice and ca.
15% in the pup tissues. This suggests that columbinate is incorporated into milk lipids of dams and is easily absorbed by
pups. The elevated ratios of 16/16∶1 and 18/18∶1 in liver and mammary gland of dams and liver and kidney of the pups from
dams fed linoleate, linolenate and columbinate suggest that each of these polyunsaturated fatty acids in the diet can inhibit
the activity of Δ9 desaturase. 相似文献
92.
In a field study P and K uptake by two corn (Zea mays L.) genotypes which differed in root growth was investigated. The effect of differences in root growth on P and K uptake was assessed using a mechanistic-mathematical model which describes nutrient uptake by growing plant roots in soil. Nitrogen was applied at 0 and 227 kg ha–1 to Pioneer 3732 and B73xMo17 corn grown on Raub silt loam (fine-silty, mixed, mesic Aquic Argiudoll) and at 227 kg N ha–1 to these two genotypes on Chalmers silt loam (finesilty, mixed, mesic, Typic Haplaquoll). Root growth and P and K uptake by the two corn genotypes was measured 31, 47, 75 and 91 d after planting on the Raub and 31, 47, 61 and 75 d after planting on the Chalmers soil.Root growth and P and K uptake by B73xMo17 was greater than that of Pioneer 3732 on N-fertilized Raub soil. On Chalmers soil the difference in root growth between the two genotypes resulted in an increase in K but not P uptake. The higher soil P level of the Chalmers appears to have offset possible differences in P uptake due to root size. There were no differences between the two genotypes in either the percentage of roots with root hairs, or the density or length of root hairs. Phosphorus and K uptake calculated with the simulation models for both corn genotypes on both soils over each of three growth periods agreed with observed P (Y = 0.68X + 1.71; r = 0.944**) and K (Y = 0.88X + 15.52; r = 0.928**) uptake. Differences in P and K uptake between B73xMo17 and Pioneer 3732 resulted primarily from the difference in root growth in the topsoil. A high correlation was found between root surface area and P (r = 0.893**) and K (r = 0.928**) uptake by both corn genotypes on both the soils.Journal paper No. 10,316 Purdue Univ. Agric. Exp. Stn., W. Lafayette, In 47906. Contribution from the Dep. of Agron. This paper was supported in part by a grant from the Tennessee Valley Authority. 相似文献
93.
Bethany Anderson Fynnette Eaton Scott W. Schwartz 《New Review of Information Networking》2015,20(1-2):3-15
The digital revolution has changed the daily work of archivists. As a result, archivists have refined their analog practices and initiated new ones to accommodate the unique information creation and access needs of users. While limitless storage and technological obsolescence may be surmountable challenges, appraisal continues to be a necessary component of this preservation enterprise. Macro-appraisal—a top-down functional assessment of an organization’s high-level decision making that defines the enduring value of specific bodies of documentary evidence of these creative or administrative processes—is used to facilitate the management of diverse bodies of born-digital records in archives and special collections. 相似文献
94.
95.
Primary focal segmental glomerulosclerosis (FSGS) is a lesion associated with a poor prognosis and results in end-stage renal disease after 5 to 10 years. Based on past experience, many nephrologists have considered primary FSGS a lesion that is steroid resistant and therefore are reluctant to offer steroids as treatment. Recent data, however, have demonstrated that patients with primary FSGS have a response to steroid therapy that is considerably better than had been described. Thus, it may be that nephrologists have been more "steroid reluctant" than the lesion is steroid resistant. To better understand this issue we review the clinical course and response to therapy in patients with primary FSGS. 相似文献
96.
AIM: To investigate which of the routinely collected claims data from the German "Legal sickness funds" on hospital utilisation may be used, in addition to that prescribed by the legislator. DESIGN: We used claims data to study a cohort of sickness fund beneficiaries who were insured during the complete year 1992 (n = 81,309). Six utilisation parameters, using the number of cases and in hospital days overall as well as diseases specific (i.e. readmission rates, in-hospital days per person with [at least] one hospital stay) were calculated. RESULTS: There are 88 persons with (at least) one hospital stay, 116 hospital cases and a total of 1306 in-hospital days per 1000 insured persons in the study cohort. The average hospital days per person (14.8 days) are ca. 30% higher than the average length of stay (11.2 days). Hospital utilisation increases with age. Hospital stays associated with ICD-239 (neoplasms of unknown origin) resulted in a higher than average number of hospital days in total although the mean length of stay is not above the average. This is due to a high readmission rate. Hospital stays associated with elective surgical procedures have a high prevalence rate but a low readmission ratio and short length of stay. CONCLUSION: The parameters related to insured persons, cases and specifically personal parameters of hospital utilisation allow a detailed analysis of hospital care; different utilisation and user patterns can be investigated and possible determinants of utilisation can be identified. After technical transformation, routine data of the sickness funds can be used to obtain information relevant for health care planners as well as for quality management. 相似文献
97.
An 11-month-old male infant with recurrent supraventricular tachycardia (SVT) was treated with oral verapamil. Shortly thereafter he developed marked changes in behavior including lethargy, intensely increased thirst and urination, and irritability when denied fluids. "Primary" polydipsia was diagnosed following an evaluation which showed no evidence of adrenal insufficiency, diabetes insipidus, diabetes mellitus, hypercalcemia, hyperosmolality, or renal disease. The symptoms resolved 1 week after verapamil was discontinued. 相似文献
98.
Rajesh Jha Nirupam Chakraborti Min Fan Justin Schwartz Carl C. Koch 《Materials and Manufacturing Processes》2017,32(10):1067-1074
A combined experimental–computational methodology for accelerated design of AlNiCo-type permanent magnetic alloys is presented with the objective of simultaneously extremizing several magnetic properties. Chemical concentrations of eight alloying elements were initially generated using a quasi-random number generator so as to achieve a uniform distribution in the design variable space. It was followed by manufacture and experimental evaluation of these alloys using an identical thermo-magnetic protocol. These experimental data were used to develop meta-models capable of directly relating the chemical composition with desired macroscopic properties of the alloys. These properties were simultaneously optimized to predict chemical compositions that result in improvement of properties. These data were further utilized to discover various correlations within the experimental dataset by using several concepts of artificial intelligence. In this work, an unsupervised neural network known as self-organizing maps was used to discover various patterns reported in the literature. These maps were also used to screen the composition of the next set of alloys to be manufactured and tested in the next iterative cycle. Several of these Pareto-optimized predictions out-performed the initial batch of alloys. This approach helps significantly reducing the time and the number of alloys needed in the alloy development process. 相似文献
99.
S Hicks G Frankel JB Kaper G Dougan AD Phillips 《Canadian Metallurgical Quarterly》1998,66(4):1570-1578
Attaching and effacing (A/E) lesion formation is central to enteropathogenic Escherichia coli (EPEC) pathogenesis. In vitro experiments with human epithelial cell lines have implicated virulence plasmid-encoded bundle-forming pili (BFP) in initial binding and intimin in intimate attachment and A/E lesion formation. This study investigated the role of BFP and intimin in EPEC interactions with pediatric small intestinal biopsy tissue in in vitro organ culture. Organ culture infections (2 to 8 h) were performed with E2348/69 (a wild-type EPEC O127:H6 clinical isolate) and E2348/69 derivatives including CVD206 (eae deficient), CVD206(pCVD438) (eae-complemented CVD206), CVD206(pCVD438/01) (expressing intimin, which is nonfunctional due to a single amino acid substitution), JPN15 (spontaneous EPEC adherence factor virulence plasmid-cured E2348/69), and 31-6-1(1) (E2348/69 with a TnphoA insertion inactivation mutation in the virulence plasmid-encoded bfpA gene). Scanning and transmission electron microscopy revealed that after 8 h E2348/69 and CVD206 (pCVD438) (both Int+ BFP+) adhered to all specimens, causing A/E lesions with surrounding microvillous elongation. JPN15 and 31-6-1(1) (both Int+ BFP-) adhered and caused A/E lesions although bacteria adhered in "flat," two-dimensional groups. CVD206 and CVD206(pCVD438/01) (both Int- BFP+) did not adhere to any sample, and no pathological tissue changes were seen. Thus, in human intestinal organ culture, BFP do not appear to be involved in the initial stages of EPEC nonintimate adhesion but are implicated in the formation of complex, three-dimensional colonies via bacterium-bacterium interactions. Intimin appears to play an essential role in establishing colonization of EPEC on pediatric small intestinal tissue. 相似文献
100.
BJ van Vlijmen NJ Pearce M Berg? B Staels JW Yates AD Gribble BC Bond MH Hofker LM Havekes PH Groot 《Canadian Metallurgical Quarterly》1998,48(4):396-402
PURPOSE: We report an investigation into the distribution of proteoglycans (PGs) in normal, organ-cultured and dextran-treated human corneas. METHODS: Immunogold labeling was carried out at the electron microscope level to localize keratan sulphate (KS), chondroitin sulphate (CS), and heparan sulphate (HS) PGs. RESULTS: High levels of labeling for CS was found in the epithelium, endothelium, and keratocytes, with light labelling present in the basement membranes and the corneal stroma. Labeling for HS was present in the epithelium, endothelium, and keratocytes, with intense labeling present at the endothelium/Descemet's membrane interface and the epithelium/Bowman's layer interface. Large filaments were also observed in these regions in cuprolinic blue-stained specimens. Keratan sulphate was present at high levels in the stroma and the basement membranes with low levels present within the keratocytes, epithelium, and endothelium. The pattern of KS labeling along the collagen fibrils in the stroma sometimes showed evidence of periodicity. Organ-cultured corneas had extensive collagen-free "lakes," the interior of which immunolabeled positively for KS and showed staining with cuprolinic blue. The lakes were greatly reduced in the dextran-treated samples. CONCLUSION: This investigation determined the ultrastructural distribution of KS, CS, and HS PGs in human cornea and showed that organ culture is associated with a change in distribution of stromal PGs. 相似文献