全文获取类型
收费全文 | 1543篇 |
免费 | 46篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 13篇 |
化学工业 | 194篇 |
金属工艺 | 9篇 |
机械仪表 | 18篇 |
建筑科学 | 32篇 |
能源动力 | 24篇 |
轻工业 | 67篇 |
水利工程 | 8篇 |
石油天然气 | 16篇 |
无线电 | 140篇 |
一般工业技术 | 222篇 |
冶金工业 | 675篇 |
原子能技术 | 46篇 |
自动化技术 | 126篇 |
出版年
2022年 | 13篇 |
2021年 | 21篇 |
2019年 | 18篇 |
2018年 | 21篇 |
2017年 | 22篇 |
2016年 | 24篇 |
2015年 | 26篇 |
2014年 | 27篇 |
2013年 | 49篇 |
2012年 | 40篇 |
2011年 | 42篇 |
2010年 | 41篇 |
2009年 | 34篇 |
2008年 | 44篇 |
2007年 | 35篇 |
2006年 | 36篇 |
2005年 | 28篇 |
2004年 | 20篇 |
2003年 | 25篇 |
2002年 | 37篇 |
2001年 | 16篇 |
2000年 | 26篇 |
1999年 | 30篇 |
1998年 | 146篇 |
1997年 | 105篇 |
1996年 | 74篇 |
1995年 | 46篇 |
1994年 | 55篇 |
1993年 | 39篇 |
1992年 | 12篇 |
1991年 | 14篇 |
1990年 | 26篇 |
1989年 | 17篇 |
1988年 | 20篇 |
1987年 | 29篇 |
1986年 | 24篇 |
1985年 | 21篇 |
1984年 | 13篇 |
1983年 | 16篇 |
1982年 | 16篇 |
1981年 | 16篇 |
1980年 | 12篇 |
1979年 | 10篇 |
1978年 | 10篇 |
1977年 | 32篇 |
1976年 | 44篇 |
1975年 | 10篇 |
1974年 | 13篇 |
1972年 | 15篇 |
1970年 | 11篇 |
排序方式: 共有1590条查询结果,搜索用时 15 毫秒
991.
ME Lowe MH Kaplan L Jackson-Grusby D D'Agostino MJ Grusby 《Canadian Metallurgical Quarterly》1998,273(47):31215-31221
The pancreas secretes several different lipases. The most abundant is pancreatic triglyceride lipase (PTL). The pancreas also synthesizes two homologues of PTL, the pancreatic lipase-related proteins 1 and 2 (PLRP1 and PLRP2). Cytotoxic T-lymphocytes also express PLRP2 under certain conditions. We sought to determine the role of PLRP2 in fat absorption and in T-cell cytotoxicity by creating a PLRP2-deficient mouse. Adult PLRP2-deficient mice had normal fat absorption. In contrast, suckling PLRP2-deficient mice had fat malabsorption evidenced by increased fecal weight, increased fecal fats, and the presence of undigested and partially digested dietary triglycerides in the feces. As a result, the PLRP2-deficient pups had a decreased rate of weight gain. To assess T cell cytotoxicity, we immunized PLRP2-deficient mice with a mastocytoma cell line, P815, and determined the ability of splenocytes from the immunized mice to kill P815 cells in a 51Cr release assay. PLRP2-deficient cells had deficient killing activity in this assay, and PLRP2-deficient splenocytes released fewer fatty acid from the target cells than did control cells. Our results provide the first evidence of a physiological function for PLRP2. PLRP2 participates in T cell cytotoxicity, and PLRP2 performs a crucial role in the digestion of dietary fats in suckling animals. 相似文献
992.
In a visual search task, participants identified the presence of a unique shape against a background of homogeneous distractors. Types of prior experience with the target, the distractor, or both were examined. In 2 experiments, a preexposure (PE) phase was followed by a test phase. The test display consisted of a target that was either target or distractor in PE or novel. Distractors were either targets or distractors in PE or novel. Reaction time was fastest for novel targets with familiar distractors, irrespective of the source of familiarity, and slowest for novel targets with novel distractors. Results are discussed in terms of attentional explanations of latent inhibition (LI) and perceptual learning and of visual search phenomena, such as novel popout. LI, previously attributed only to a deficit in the stimulus preexposed group, may also be due to enhanced performance in the nonpreexposed group. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
993.
BACKGROUND: Yersinia enterocolitica is frequently identified in cases of bacterial sepsis due to red cell transfusion. One of the features that makes Y. enterocolitica particularly dangerous is that, unlike most other bacterial contaminants of blood components, this organism can actively multiply in currently recommended refrigerator temperatures (1-6 degrees C). The effect of a colder than normal storage temperature on Y. enterocolitica growth was investigated to determine whether bacteria growth could be reduced or inhibited at 0 degree C. STUDY DESIGN AND METHODS: Twenty-four units of freshly collected donated blood were obtained. Three sets of 7 units each were inoculated with Y. enterocolitica O:3, Y. enterocolitica O:20, and Y. enterocolitica O:5, 27, respectively. The remaining 3 units served as uninoculated controls. Each of the 24 bags was split into two equal aliquots, with one aliquot stored at 4 degrees C and the other at 0 degree C. Bacteria growth was measured twice weekly for 6 weeks. Endotoxin and hemoglobin levels were also measured at selected intervals. RESULTS: Bacteria growth was detected earlier and in higher concentrations in the aliquots stored at 4 degrees C. Twenty-two of the 42 inoculated aliquots had measureable bacteria growth. Thirteen aliquots had been maintained at 4 degrees C, and nine had been stored at 0 degree C. Sixteen of these 22 aliquots were matched pairs. Exponential growth was detected after 14 to 32 days in the 4 degrees C aliquots and after 28 to 39 days in the 0 degree C aliquots. Final bacteria counts were much higher in the 4 degrees C aliquots (10(5)-10(14) colony-forming units/mL) than in the 0 degree C aliquots (10(1)-10(4) colony-forming units/mL) on Day 42. Endotoxin was present in all 13 of the 4 degrees C aliquots with actively growing Y. enterocolitica. CONCLUSION: Storage of red cells at 0 degree C markedly prolongs the time required for Y. enterocolitica to achieve exponential grwoth and results in lower concentrations of bacteria. 相似文献
994.
JD Duncan SD Moss DJ Bandy K Manwaring AM Kaplan EM Reiman K Chen MA Lawson DL Wodrich 《Canadian Metallurgical Quarterly》1997,26(3):144-156
Successful surgical management of a neoplastic or nonneoplastic seizure focus in close proximity to or within eloquent brain areas relies on precise delineation of the relationship between the lesion and functional brain areas. The aim of this series was to validate the usefulness and test the efficacy of noninvasive presurgical PET mapping of eloquent brain areas to predict surgical morbidity and outcome in children with seizures. To identify eloquent brain areas in 15 children (6 female and 9 male; mean age 11 years) with epileptogenic lesions PET images of regional cerebral blood flow were performed following the administration of [(15)O]water during motor, visual, articulation, and receptive language tasks. These images with coregistered magnetic resonance (MR) images were then used to delineate the anatomic relationship of a seizure focus to eloquent brain areas. Additional PET images using [18F]fluoro-2-deoxy-D-glucose (FDG) and [11C]methionine (CMET) were acquired to help localize the seizure focus, as well as characterize the lesion. Patient surgical management decisions were based on PET mapping in combination with coregistered MR images, PET-FDG findings, and the anatomic characteristics of the lesion. At follow-up 1-26 months after surgery, all patients that underwent temporal lobectomy (9 patients) and extratemporal resection (4 patients) for a neoplastic or nonneoplastic seizure focus are seizure-free with minimal postoperative morbidity. Of prime importance, no child sustained a postoperative speech or language deficit. PET imaging was also well tolerated without procedural complications. Based on PET mapping, a nonoperative approach was used for 2 children and a biopsy only was used in one child. When cortical injury involved prenatally determined eloquent cortex, PET demonstrated reorganization of language areas to new adjacent areas or even to the contralateral hemisphere. Integration of anatomical and functional data enhanced the surgical safety, defined optimal surgical approach, delineated the seizure focus from eloquent brain areas, facilitated maximum resection and optimized the timing of surgery, thereby minimizing surgical morbidity while maximizing surgical goals. PET measurements of FDG and CMET uptake were also helpful in localizing the seizure focus and grading the tumors. PET used for brain mapping in children provides the surgeon with strategic preoperative information not readily attainable with traditional invasive Wada testing or intraoperative cortical stimulation. PET mapping may also improve the outcome of extratemporal resections by allowing aggressive seizure focus resection. In addition, serial brain maps may optimize timing for surgical intervention by demonstrating reorganization of eloquent cortex often seen in younger children after cortical injury. Our results suggest that noninvasive presurgical brain mapping has the potential to reduce risk and improve neurologic outcome. 相似文献
995.
DNA solution of the maximal clique problem 总被引:1,自引:0,他引:1
The maximal clique problem has been solved by means of molecular biology techniques. A pool of DNA molecules corresponding to the total ensemble of six-vertex cliques was built, followed by a series of selection processes. The algorithm is highly parallel and has satisfactory fidelity. This work represents further evidence for the ability of DNA computing to solve NP-complete search problems. 相似文献
996.
Atrial fibrillation (AF) remains a challenge to medical therapy. Over the past several years, a variety of experimental models of AF have been developed. These have provided insights into mechanisms underlying AF and antiarrhythmic drug action against the arrhythmia. A variety of drugs effective against clinical AF, including flecainide, propafenone, procainamide, and sotalol, have been found to terminate experimental AF. All of these agents appear to act by prolonging the wavelength for atrial reentry at rapid rates, thereby increasing the size and decreasing the number of functional circuits maintaining the arrhythmia. While the ability to terminate AF is determined by refractoriness prolongation at rapid rates, refractoriness prolongation at slow rates (e.g., sinus rhythm) can prevent AF induction by premature beats. Thus, drugs with strong reverse use-dependence (like sotalol) may be much more effective in preventing than in terminating AF. Spacial heterogeneity in refractoriness is an important contributor to AF occurrence in some models, particularly vagal AF, and is reduced by some (but not all) drugs that terminate AF. New insights are being gained into mechanisms of electrical remodeling, which promotes AF maintenance when rapid atrial rates are maintained, such as during AF. This electrical remodeling may be an interesting novel target for therapy of AF. Insights into AF mechanisms obtained in experimental models of AF should help in the development of new and improved therapeutic approaches. 相似文献
997.
AL Moreira LG Corral W Ye B Johnson D Stirling GW Muller VH Freedman G Kaplan 《Canadian Metallurgical Quarterly》1997,13(10):857-863
Thalidomide is currently being evaluated for efficacy in alleviating some manifestations of HIV-1 infection. To determine whether thalidomide has any direct effects on HIV-1 infection, we investigated the effect of thalidomide and also of three structural analogs of thalidomide on HIV-1 replication in vitro in human monocyte-derived macrophages. The thalidomide analogs were previously shown to inhibit TNF-alpha production in vitro at much lower concentrations than thalidomide. In HIV-1-infected macrophages treated with thalidomide or thalidomide analogs, viral replication was reduced by 60 to 80% as determined by measuring viral RT activity in the culture supernatants. In all experiments the analogs inhibited HIV-1 replication more efficiently than did thalidomide. The drugs also reduced HIV-1 gag mRNA expression. Furthermore, the drugs caused a decrease in NF-kappaB-binding activity in nuclear extracts of HIV-1-infected macrophages. The role of NF-kappaB in the drug-induced inhibition of HIV-1 replication was confirmed using an NF-kappaB-defective mutant virus to infect macrophages. 相似文献
998.
I. G. Maryasev V. N. Koptelov F. S. Kaplan O. R. Grishina 《Refractories and Industrial Ceramics》2003,44(5):338-342
Results for periclase-carbon materials with different proportion of the finely dispersed fraction tested for linear expansion at 20 – 1420°C under argon are reported. The composition of finely dispersed fraction (varying in proportion from 100% periclase to 100% alumomagnesian spinel) and the carbonization regime are factors that determine the thermal expansion of the materials studied. A hysteretic behavior of the linear expansion curves is established and shown to be related to sintering processes and volumetric phase transformations. The data obtained can be used to optimize the composition and heat treatment of periclase-carbon refractory materials. 相似文献
999.
1000.
The Na-(K)-Cl cotransporter family in the mammalian kidney: molecular identification and function(s)
A new solute carrier gene family, SLC12, was recently described based on the molecular identification of three electroneutral Na-(K)-Cl cotransport proteins. In mammals, these proteins are encoded by three distinct but related genes: SLC12A1, SLC12A2, SLC12A3, which are located on different chromosomes. Although the expression patterns of these three cotransport proteins differ significantly, all of them are expressed in the mammalian kidney and participate in several important aspects of renal function. This review summarizes the information learned from the molecular identification of these cotransporters, evaluates the patterns of expression within the kidney, and discusses the roles that these cotransporters play in renal physiology and pathophysiology. 相似文献