全文获取类型
收费全文 | 874篇 |
免费 | 6篇 |
专业分类
电工技术 | 3篇 |
化学工业 | 28篇 |
金属工艺 | 9篇 |
机械仪表 | 7篇 |
建筑科学 | 3篇 |
能源动力 | 7篇 |
轻工业 | 13篇 |
无线电 | 11篇 |
一般工业技术 | 32篇 |
冶金工业 | 754篇 |
原子能技术 | 2篇 |
自动化技术 | 11篇 |
出版年
2020年 | 4篇 |
2019年 | 2篇 |
2018年 | 2篇 |
2016年 | 3篇 |
2015年 | 4篇 |
2014年 | 2篇 |
2013年 | 9篇 |
2012年 | 2篇 |
2011年 | 6篇 |
2009年 | 9篇 |
2008年 | 7篇 |
2007年 | 9篇 |
2006年 | 5篇 |
2005年 | 9篇 |
2004年 | 6篇 |
2003年 | 9篇 |
2002年 | 3篇 |
2001年 | 5篇 |
2000年 | 7篇 |
1999年 | 22篇 |
1998年 | 229篇 |
1997年 | 132篇 |
1996年 | 90篇 |
1995年 | 56篇 |
1994年 | 45篇 |
1993年 | 45篇 |
1992年 | 7篇 |
1991年 | 6篇 |
1990年 | 3篇 |
1989年 | 6篇 |
1988年 | 9篇 |
1987年 | 6篇 |
1986年 | 15篇 |
1985年 | 5篇 |
1984年 | 3篇 |
1983年 | 4篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1980年 | 8篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1977年 | 20篇 |
1976年 | 35篇 |
1974年 | 2篇 |
1971年 | 3篇 |
1967年 | 2篇 |
1958年 | 2篇 |
1957年 | 1篇 |
1955年 | 3篇 |
1954年 | 1篇 |
排序方式: 共有880条查询结果,搜索用时 46 毫秒
51.
OBJECTIVE: To examine the occurrence of elevated personality disorder (PD) dimensional scores in a community sample of young adults as a function of the occurrence of Axis I disorders through age 18 years. METHOD: 299 individuals who had been interviewed regarding Axis I disorders twice while in adolescence (first when 14 through 18 years of age) were carefully assessed regarding Axis I and II psychopathology at age 24. RESULTS: The prevalence of PD diagnoses was relatively low (3.8% in participants with a history of Axis I versus 1.7% in participants with no Axis I history). The occurrence of all four Axis I diagnostic categories (major depression, anxiety disorders, disruptive behavior disorders, substance use disorders) in childhood and adolescence was associated with elevated PD dimensional scores. The likelihood of elevated PD dimensional scores increased as a function of the number of Axis I disorders. Elevated PD scores were significantly associated with a negative course of major depression. CONCLUSIONS: Although the rates of PDs were low, the findings suggest a substantial degree of association between early-onset Axis I disorders and Axis II psychopathology in young adulthood. More research is needed to develop assessment and treatment recommendations addressing the early manifestations of PDs. 相似文献
52.
53.
Matsumoto David; Haan Norma; Yabrove Gary; Theodorou Paola; Carney Caroline Cooke 《Canadian Metallurgical Quarterly》1986,22(5):663
The moral acts of 19 dyads of 4-yr-olds in a cognitively simplified version of Prisoner's Dilemma game were analyzed in relationship to their friendship, emotions, and processes of conflict resolution. Degree of friendship was rated by teachers; 2 sociologists used a Q-sort of group processes to describe the dyads' interactions. The emotions of each S were coded from videotape independently of his/her partner's and with the sound turned off. Moral acts were categorically identified as equalization, reparation, stalemate, default, and betrayal. These acts were also assigned scale scores on a dimension of moral sensitivity that was independently derived from separate work with 143 undergraduates, who judged the 5 acts in all possible paired comparisons and then rated the moral difference between each pair. These data almost perfectly fitted a model of increasing monotonic function. The degree of friendship between the dyads and their interactive processes—group orientation, positive emotional tone, and active involvement—were positively related to sensitive moral action. Their emotions were related to concurrent acts, and more importantly, predicted their subsequent acts even though they seldom talked about morality. Results suggest that if social scientists' search for practical morality is to be successful, emotional communication needs to be considered. (30 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
54.
Examination of a Structural Model of Peptidomimicry by Cyclic Acyldepsipeptide Antibiotics in Their Interaction with the ClpP Peptidase
下载免费PDF全文
![点击此处可从《Chembiochem : a European journal of chemical biology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dr. Daniel W. Carney Dr. Karl R. Schmitz Anthony C. Scruse Prof. Dr. Robert T. Sauer Prof. Dr. Jason K. Sello 《Chembiochem : a European journal of chemical biology》2015,16(13):1875-1879
The cyclic acyldepsipeptide (ADEP) antibiotics act by binding the ClpP peptidase and dysregulating its activity. Their exocyclic N‐acylphenylalanine is thought to structurally mimic the ClpP‐binding, (I/L)GF tripeptide loop of the peptidase's accessory ATPases. We found that ADEP analogues with exocyclic N‐acyl tripeptides or dipeptides resembling the (I/L)GF motif were weak ClpP activators and had no bioactivity. In contrast, ADEP analogues possessing difluorophenylalanine N‐capped with methyl‐branched acyl groups—like the side chains of residues in the (I/L)GF motifs—were superior to the parent ADEP with respect to both ClpP activation and bioactivity. We contend that the ADEP's N‐acylphenylalanine moiety is not simply a stand‐in for the ATPases' (I/L)GF motif; it likely has physicochemical properties that are better suited for ClpP binding. Further, our finding that the methyl‐branching on the acyl group of the ADEPs improves activity opens new avenues for optimization. 相似文献
55.
56.
1. Travellers to high altitude often complain of paroxysmal cough, which has not been previously investigated. We recorded overnight cough frequency and cough-receptor sensitivity to inhaled citric acid in a group of climbers travelling to 5300 m or higher. 2. Cough frequency, monitored in ten subjects, increased from a median of 0 coughs at sea level (range 0-1) to 5 coughs at 5000 m (range 0-13) and to over 60 coughs in subjects ascending to 7000 m. Citric acid cough threshold, measured in 42 subjects, was unchanged on arrival at 5300 m compared with sea level (geometric mean difference 1.26, 95% confidence intervals 0.84-1.89, P = 0.25), but was significantly reduced after 6 days, or more, at altitude compared with sea level (geometric mean difference 2.2, 95% confidence intervals 1.54-3.15, P = 0.0002). Cough threshold was not related to symptoms of acute mountain sickness, oxygen saturation, carbon dioxide tension or lung function. 3. These results indicate an increase in cough and cough-receptor sensitivity after some days at altitude. This may be due to respiratory tract damage from breathing cold dry air at increased ventilatory rates. Other explanations, such as sub-clinical pulmonary oedema or an effect on the cough centre of acclimatization to altitude, cannot be excluded. 相似文献
57.
1. While it is believed that the mammalian distal nephron is not involved in uric acid transport, this has not been directly evaluated. Nevertheless, some studies are consistent with significant distal nephron transport. 2. As uric acid transport in man may be similar to the rat, undirectional uric acid permeability was evaluated by perfusion of the isolated rat papillary collecting duct. 3. Uric acid permeability was 0.61 +/- 0.04 micron/s, which was similar to sodium permeability (0.66 +/- 0.05 micron/s) but was less than chloride permeability (0.93 +/- 0.07 micron/s) and markedly less than water permeability (4.81 +/- 0.21 micron/s). Uric acid permeability was not changed following the addition of a maximal antidiuretic concentration of arginine vasopressin (200 microU/mL), nor was it changed by altering the uric acid concentration in the perfusate and bath. 4. These results demonstrate that the papillary collecting duct is permeable to uric acid. The coefficient of transport is sufficiently low and insensitive to arginine vasopressin and uric acid concentrations to suggest that any transport that occurs is probably passive and only of minor physiological significance. 相似文献
58.
When plane-polarized light impinges on a solution of optically active molecules, the polarization of the light that emerges is rotated. This simple phenomenon arises from the interaction of light with matter and is well understood, in principle, van't Hoff's rule of optical superposition correlates the molar rotation with the individual contributions to optical activity of isolated centers of asymmetry. This straightforward empirical additivity rule is rarely used for structure elucidation nowadays because of its limitations in the assessment of conformationally restricted or interacting chiral centers. However, additivity can be used successfully to assign the configuration of complex natural products such as hennoxazole A if appropriate synthetic partial structures are available. Therefore, van't Hoff's principle is a powerful stereochemical complement to natural products' total synthesis. The quest for reliable quantitative methods to calculate the angle of rotation a priori has been underway for a long time. Both classical and quantum methods for calculating molar rotation have been developed. Of particular practical importance for determining the absolute structure of molecules by calculation is the manner in which interactions between multiple chiral centers in a single molecule are included, leading to additive or non-additive optical rotation angles. This problem is addressed here using semi-empirical electronic structure models and the Rosenfeld equation. 相似文献
59.
DA Emmerson KA Turner DN Foster NB Anthony KE Nestor 《Canadian Metallurgical Quarterly》1997,76(11):1563-1568
The activity of ornithine decarboxylase (ODC), an enzyme associated with cellular growth and protein synthesis, was examined in breast muscle, liver, and intestinal tissues of turkeys during a short-term period of feed withdrawal (FW) and following refeeding. Turkeys from a randombred control line were reared under standard management practices to 3 wk of age in battery brooders. Feed was then withdrawn from FW birds for a 48-h period, after which feed was consumed ad libitum. Control birds consumed feed ad libitum throughout the test period. Tissues were collected from 12 birds per treatment following 24 and 48 h of FW and at 6, 12, 24, and 48 h following refeeding for later determination of tissue ODC activity. Activity of ODC was greater in tissue from the small intestine than in liver tissue and both had greater activity than that exhibited by breast muscle. Short-term FW and refeeding produced differential responses in ODC activity of the three tissues examined. Feed withdrawal resulted in a reduction of ODC activity in intestinal tissue, whereas activity was unaffected for liver or breast muscle tissues. Compensatory increases in ODC activity were observed in liver and intestinal tissues; however, the increase was both more rapid and transitory in small intestine than in liver tissue. The ODC activity in breast muscle was largely unaffected by short-term FW and refeeding. Patterns of ODC activity in liver during FW and refeeding closely resembled patterns observed for absolute and relative liver weight. Thus, the results of the present experiment demonstrate that short-term FW and refeeding influence underlying growth mechanisms of supply organs, such as hepatic and intestinal tissue, in addition to affecting overall growth and muscle development. 相似文献
60.
M Winey CL Mamay ET O'Toole DN Mastronarde TH Giddings KL McDonald JR McIntosh 《Canadian Metallurgical Quarterly》1995,129(6):1601-1615
The three dimensional organization of microtubules in mitotic spindles of the yeast Saccharomyces cerevisiae has been determined by computer-aided reconstruction from electron micrographs of serially cross-sectioned spindles. Fifteen spindles ranging in length from 0.6-9.4 microns have been analyzed. Ordered microtubule packing is absent in spindles up to 0.8 micron, but the total number of microtubules is sufficient to allow one microtubule per kinetochore with a few additional microtubules that may form an interpolar spindle. An obvious bundle of about eight interpolar microtubules was found in spindles 1.3-1.6 microns long, and we suggest that the approximately 32 remaining microtubules act as kinetochore fibers. The relative lengths of the microtubules in these spindles suggest that they may be in an early stage of anaphase, even though these spindles are all situated in the mother cell, not in the isthmus between mother and bud. None of the reconstructed spindles exhibited the uniform populations of kinetochore microtubules characteristic of metaphase. Long spindles (2.7-9.4 microns), presumably in anaphase B, contained short remnants of a few presumed kinetochore microtubules clustered near the poles and a few long microtubules extending from each pole toward the spindle midplane, where they interdigitated with their counterparts from the other pole. Interpretation of these reconstructed spindles offers some insights into the mechanisms of mitosis in this yeast. 相似文献