全文获取类型
收费全文 | 4805篇 |
免费 | 41篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 6篇 |
化学工业 | 151篇 |
金属工艺 | 3篇 |
机械仪表 | 3篇 |
建筑科学 | 36篇 |
矿业工程 | 2篇 |
能源动力 | 13篇 |
轻工业 | 106篇 |
水利工程 | 31篇 |
无线电 | 59篇 |
一般工业技术 | 110篇 |
冶金工业 | 4250篇 |
原子能技术 | 3篇 |
自动化技术 | 74篇 |
出版年
2023年 | 11篇 |
2022年 | 22篇 |
2021年 | 30篇 |
2020年 | 25篇 |
2019年 | 21篇 |
2018年 | 19篇 |
2017年 | 14篇 |
2016年 | 19篇 |
2015年 | 15篇 |
2014年 | 18篇 |
2013年 | 39篇 |
2012年 | 47篇 |
2011年 | 64篇 |
2010年 | 36篇 |
2009年 | 31篇 |
2008年 | 33篇 |
2007年 | 34篇 |
2006年 | 18篇 |
2005年 | 24篇 |
2004年 | 24篇 |
2003年 | 24篇 |
2002年 | 9篇 |
2001年 | 6篇 |
2000年 | 9篇 |
1999年 | 132篇 |
1998年 | 1243篇 |
1997年 | 776篇 |
1996年 | 460篇 |
1995年 | 260篇 |
1994年 | 216篇 |
1993年 | 256篇 |
1992年 | 37篇 |
1991年 | 39篇 |
1990年 | 58篇 |
1989年 | 50篇 |
1988年 | 73篇 |
1987年 | 52篇 |
1986年 | 47篇 |
1985年 | 45篇 |
1983年 | 6篇 |
1982年 | 23篇 |
1981年 | 30篇 |
1980年 | 44篇 |
1979年 | 5篇 |
1978年 | 4篇 |
1977年 | 124篇 |
1976年 | 244篇 |
1975年 | 6篇 |
1973年 | 4篇 |
1955年 | 5篇 |
排序方式: 共有4847条查询结果,搜索用时 15 毫秒
71.
RM Hendry CV Hanson V Bongertz M Morgado A Duarte J Casseb L Brigido E Sabino R Diaz B Galv?o-Castro 《Canadian Metallurgical Quarterly》1996,91(3):347-348
The influence of noncompetitive (MK-801), competitive (AP-7) and the antagonist of polyamines site of NMDA receptor (arcaine) on the central activity of angiotensin II (A II) was studied. The open field test, conditioning of active avoidance responses (CARs) and passive avoidance situation was used to investigate learning and memory in rats. All used antagonists decreased beneficial action of A II on these processes. 相似文献
72.
RM Summers J Andrasko-Bourgeois IM Feuerstein SC Hill EC Jones MK Busse B Wise KE Bove BA Rishforth E Tucker TL Spray JM Hoeg 《Canadian Metallurgical Quarterly》1998,98(6):509-518
Hepatitis C chronically infects approximately 1.5% of Americans and is the most common clinical problem facing hepatologists. Since the virus was initially described in 1989, development of an effective therapy has been challenging. Although several different therapeutic agents have been used, no therapy has been shown to reliably eradicate the virus. Interferon-alpha, a cytokine with immunostimulatory and anti-viral properties, has become the therapy of choice for patients with chronic hepatitis C infection. Trials assessing the efficacy of interferon-alpha have characterized host and viral factors predictive of responses to treatment. A thorough understanding of these predictive factors is requisite to providing cost-effective therapeutic decisions for the patient with chronic hepatitis C infection. 相似文献
73.
Previous studies have shown that Tetrahymena citrate synthase and the Tetrahymena 14-nm filament protein are encoded by a single gene and translated from one species of mRNA, and that they are identical in terms of molecular weight, antigenicity, and some enzymatic properties. In this study, using two-dimensional gel electrophoresis, we demonstrated that the citrate synthase comprised pI 7.7 and 8.0 isoforms, while the 14-nm filament protein comprised three isoforms with isoelectric points of 7.7, 8.0, and 8.4. The amino acid sequences of the NH2-terminal portions of all isoforms were identical and the peptide maps with V8 protease were almost the same. In addition, when the citrate synthase activity of each isoform was measured after separation by non-urea isoelectric focusing without denaturing treatment, the pI 7.7 and/or pI 8.0 isoforms exhibited the citrate synthase activity, but the pI 8.4 isoform only found for the 14-nm filament protein did not possess this activity. These results suggest that the polymorphism of these isoforms is caused by some posttranslational modifications, and that it may have resulted in the different compartmentalization and functions of Tetrahymena citrate synthase and the 14-nm filament protein. 相似文献
74.
J Seoane K Trinh RM O'Doherty AM Gómez-Foix AJ Lange CB Newgard JJ Guinovart 《Canadian Metallurgical Quarterly》1997,272(43):26972-26977
Glucose-6-phosphatase (G6Pase) catalyzes the hydrolysis of glucose 6-phosphate (Glu-6-P) to free glucose and, as the last step in gluconeogenesis and glycogenolysis in liver, is thought to play an important role in glucose homeostasis. G6Pase activity appears to be conferred by a set of proteins localized to the endoplasmic reticulum, including a glucose-6-phosphate translocase, a G6Pase phosphohydrolase or catalytic subunit, and glucose and inorganic phosphate transporters in the endoplasmic reticulum membrane. In the current study, we used a recombinant adenovirus containing the cDNA encoding the G6Pase catalytic subunit (AdCMV-G6Pase) to evaluate the metabolic impact of overexpression of the enzyme in primary hepatocytes. We found that AdCMV-G6Pase-treated liver cells contain significantly less glycogen and Glu-6-P, but unchanged UDP-glucose levels, relative to control cells. Further, the glycogen synthase activity state was closely correlated with Glu-6-P levels over a wide range of glucose concentrations in both G6Pase-overexpressing and control cells. The reduction in glycogen synthesis in AdCMV-G6Pase-treated hepatocytes is therefore not a function of decreased substrate availability but rather occurs because of the regulatory effects of Glu-6-P on glycogen synthase activity. We also found that AdCMV-G6Pase-treated-cells had significantly lower rates of lactate production and [3-3H]glucose usage, coupled with enhanced rates of gluconeogenesis and Glu-6-P hydrolysis. We conclude that overexpression of the G6Pase catalytic subunit alone is sufficient to activate flux through the G6Pase system in liver cells. Further, hepatocytes treated with AdCMV-G6Pase exhibit a metabolic profile resembling that of liver cells from patients or animals with non-insulin-dependent diabetes mellitus, suggesting that dysregulation of the catalytic subunit of G6Pase could contribute to the etiology of the disease. 相似文献
75.
MD Medlock JR Madsen PD Barnes DS Anthony LE Cohen RM Scott 《Canadian Metallurgical Quarterly》1997,27(3):121-128
There are many in vivo animal models for studying airway mucus secretion and hypersecretion, each with advantages and disadvantages. Use of a particular test system will depend upon the aspect of secretion to be modelled. Airway hypersecretory diseases exhibit chronic mucus hypersecretion, of which the clinical impact is predominantly in the distal airways. The majority of documented test preparations study acute secretion, invariably using tracheal preparations, but have been invaluable in elucidating the normal physiology of airway mucus secretion. Chronic models of the hypersecretory state in the distal airways have been developed, but are predominantly histologic in nature (for example quantification of increased goblet cell number). There are few investigations of mucus hypersecretion. Examination of the 'antisecretory' potential of pharmaceutical compounds has been investigated predominantly in chronic histologic models with the drug being given 'prophylactically' rather than 'therapeutically'. Refinement of chronic hypersecretory models should lead to elucidation of the connection between airway irritation, inflammation, MUC gene expression, mucous cell hyperplasia/metaplasia, airway hypersecretion and bronchial hypersecretory disease. 相似文献
76.
77.
RM Nelson 《Canadian Metallurgical Quarterly》1997,13(3):691-701
This article discusses ethical issues that exist each and every day in interactions with patients, families, and fellow workers in the ICU, even in the absence of overt conflict or controversy. The creation of an ethical working environment in the ICU is a necessary precondition for dealing with the ethical issues raised by specific issues such as cardiopulmonary resuscitation, the limitation or withdrawal of life-sustaining treatment, the special care of children with disabilities, brain death, and organ procurement, and triage. The creation of an ethical working environment requires developing a collaborative relationship with patients, families, staff, and other health care professionals. 相似文献
78.
Both hypo- and hyperthyroidism are characterised by exercise intolerance. In hypothyroidism, inadequate cardiovascular support appears to be the principal factor involved. Insufficient skeletal muscle blood flow compromises exercise capacity via reduced oxygen delivery, and endurance through decreased delivery of blood-borne substrates. The latter effect results in increased dependence on intramuscular glycogen. Additionally, decreased mobilisation of free fatty acids from adipose tissue and, consequently, lower plasma free fatty acid levels compound the problem of reduced lipid delivery to active skeletal muscle in the hypothyroid state. In contrast, cardiovascular support is enhanced in hyperthyroidism, implicating other factors in exercise tolerance. Greater reliance on muscle glycogen appears to be the primary reason for decreased endurance. Biochemical changes with hyperthyroidism that would favour enhanced flux through glycolysis may account for this dependence on glycogen. Deviations from normal thyroid function, and the ensuing exercise tolerance, require appropriate medical therapy to attain euthyroid status. 相似文献
79.
80.
Over a period of 4.5 years, 14 patients with frontoethmoidal meningoencephaloceles were treated. Most patients came from Northern Namibia. Precise delineation of all cranial abnormalities was obtained by modern imaging techniques, and specific patterns of cerebral abnormality were found. The malformation was corrected in a single stage, and significant modifications have been developed to render the procedure simpler and safer. Information from our series favors delayed neural tube closure as the primary pathogenesis of the defect and suggests a common teratogen as the most probable etiological agent. Our experience leads us to advocate early correction of even small defects. 相似文献