全文获取类型
收费全文 | 1354篇 |
免费 | 0篇 |
专业分类
化学工业 | 3篇 |
能源动力 | 1篇 |
轻工业 | 2篇 |
无线电 | 5篇 |
一般工业技术 | 2篇 |
冶金工业 | 1340篇 |
自动化技术 | 1篇 |
出版年
2016年 | 1篇 |
2014年 | 1篇 |
2012年 | 1篇 |
2011年 | 1篇 |
2004年 | 1篇 |
2003年 | 3篇 |
1999年 | 35篇 |
1998年 | 353篇 |
1997年 | 225篇 |
1996年 | 140篇 |
1995年 | 67篇 |
1994年 | 85篇 |
1993年 | 81篇 |
1992年 | 10篇 |
1991年 | 28篇 |
1990年 | 25篇 |
1989年 | 23篇 |
1988年 | 37篇 |
1987年 | 25篇 |
1986年 | 12篇 |
1985年 | 19篇 |
1983年 | 4篇 |
1982年 | 7篇 |
1981年 | 8篇 |
1980年 | 8篇 |
1978年 | 3篇 |
1977年 | 54篇 |
1976年 | 90篇 |
1975年 | 3篇 |
1970年 | 1篇 |
1965年 | 1篇 |
1955年 | 2篇 |
排序方式: 共有1354条查询结果,搜索用时 15 毫秒
41.
KG Sutton C Siok A Stea GW Zamponi SD Heck RA Volkmann MK Ahlijanian TP Snutch 《Canadian Metallurgical Quarterly》1998,54(2):407-418
Peptide toxins have proved to be useful agents, both in discriminating between different components of native calcium channel currents and in the molecular isolation and designation of their cloned channel counterparts. Here, we describe the isolation and characterization of the biochemical and physiological properties of a novel 74-amino acid peptide toxin (DW13.3) extracted from the venom of the spider Filistata hibernalis. The subtype specificity of DW13.3 was investigated using calcium channel currents recorded from two separate expression systems and several different cultured mammalian cell preparations. Overall, DW13.3 potently blocked all native calcium channel currents studied, with the exception of T-type currents recorded from GH3 cells. Examination of transiently expressed calcium channels in oocytes showed that DW13.3 had the highest affinity for alpha1A, followed by alpha1B > alpha1C > alpha1E. The affinity of DW13.3 for alpha1B N-type currents varied by 10-fold between expressed channels and native currents. Although block occurred in a similar 1:1 manner for all subtypes, DW13.3 produced a partial block of both alpha1A currents and P-type currents in cerebellar Purkinje cells. Selective occlusion of the P/Q-type channel ligand omega-conotoxin MVIIC (but not omega-agatoxin IVA) from its binding site in Purkinje neurons suggests that DW13.3 binds to a site close to the pore of the channel. The inhibition of different subtypes of calcium channels by DW13.3 reflects a common "macro" binding site present on all calcium channels except T-type. 相似文献
42.
As part of the search for anticomplementary active components from natural products, the anticomplementary properties of methanolic extracts from the flower buds of Magnoliafargesii have been investigated. Bioassay-guided chromatographic separation of the active constituents led to the isolation of compound 1, whose structure was identified by spectroscopic methods to be kaempferol 3-O-beta-D-(6"-O-coumaroyl)glucopyranoside (tiliroside). Tiliroside showed very potent anti-complement activity (IC50=5.4 x 10(-5) M) on the classical pathway of the complement system, even higher than rosmarinic acid, which is a well-known inhibitor against the complement system. On the other hand, the hydrolysates of tiliroside, kaempferol, astragalin and p-coumaric acid showed very weak activity on this system. 相似文献
43.
GW Gao SH Lin YF Lin LK Diang KC Lu FC Yu SD Shieh 《Canadian Metallurgical Quarterly》1996,57(6):438-442
Despite a general national decline in criminal activities in the 1990s, juvenile criminal offenses continue to increase, (including violent, property, and delinquency acts). In addition increased numbers of children are being held in juvenile jails. It is all but impossible for pediatric health providers to think that "their patients" and "their practices" are immune from the epidemic of crime that affects and is caused by "just kids." 相似文献
44.
In response to the increasing trend toward community health care, a model of training that prepares students for community practice was incorporated into the occupational therapy curriculum at the University of Southern California. During academic training students are placed in a part-time community assignment where no occupational therapy services are offered. Training students for the role of community health specialist produces a dilemma for curriculum design. A balance must be achieved between providing traditional clinical content and providing the knowledge and expertise necessary for community practice. However, this training is considered necessary for maintaining the viability of the profession in a changing health system. Significantly, during the four-year period using this model, many graduates have sought employment in "nontraditional" community roles. 相似文献
45.
GW Prager JM Breuss S Steurer J Mihaly BR Binder 《Canadian Metallurgical Quarterly》2004,103(3):955-962
Vascular endothelial growth factor (VEGF) is the pivotal angiogenic growth factor activating endothelial cells to migrate, proliferate, and form capillary tubes. For an ordered endothelial cell migration, tissue invasion, and degradation of the extracellular matrix, proteolytic machinery is indispensable. Such machinery, suitable for localized proteolysis, is provided by the prourokinase-urokinase-plasmin system. Prourokinase (pro-uPA), the initial component of this system, is, however, synthesized in its inactive precursor form and as such bound to its cellular receptor uPAR. Here we identify a mechanism via which VEGF(165) interacting with its receptor VEGFR-2 rapidly induces prourokinase activation that is dependent on a change in integrin affinity, activation of matrix metalloproteinase 2 (MMP-2), and pro-uPA being bound to its surface receptor uPAR. This VEGF-induced pro-uPA activation on endothelial cells is responsible for VEGF-dependent local fibrinolytic activity and might be one of the initial steps in the angiogenic process. 相似文献
46.
C Mu-Forster R Huang JR Powers RW Harriman M Knight GW Singletary PL Keeling BP Wasserman 《Canadian Metallurgical Quarterly》1996,111(3):821-829
Antibodies were used to probe the degree of association of starch biosynthetic enzymes with starch granules isolated from maize (Zea mays) endosperm. Graded washings of the starch granule, followed by release of polypeptides by gelatinization in 2% sodium dodecyl sulfate, enables distinction between strongly and loosely adherent proteins. Mild aqueous washing of granules resulted in near-complete solubilization of ADP-glucose pyrophosphorylase, indicating that little, if any, ADP-glucose pyrophosphorylase is granule associated. In contrast, all of the waxy protein plus significant levels of starch synthase I and starch branching enzyme II (BEII) remained granule associated. Stringent washings using protease and detergent demonstrated that the waxy protein, more than 85% total endosperm starch synthase I protein, and more than 45% of BEII protein were strongly associated with starch granules. Rates of polypeptide accumulation within starch granules remained constant during endosperm development. Soluble and granule-derived forms of BEII yielded identical peptide maps and overlapping tryptic fragments closely aligned with deduced amino acid sequences from BEII cDNA clones. These observations provide direct evidence that BEII exits as both soluble and granule-associated entities. We conclude that each of the known starch biosynthetic enzymes in maize endosperm exhibits a differential propensity to associate with, or to become irreversibly entrapped within, the starch granule. 相似文献
47.
48.
A Messerschmidt L Prade SJ Kroes J Sanders-Loehr R Huber GW Canters 《Canadian Metallurgical Quarterly》1998,95(7):3443-3448
The rack-induced bonding mechanism of metals to proteins is a useful concept for explaining the generation of metal sites in electron transfer proteins, such as the blue copper proteins, that are designed for rapid electron transfer. The trigonal pyramidal structure imposed by the protein with three strong equatorial ligands (one Cys and two His) provides a favorable geometry for both cuprous and cupric oxidation states. However, the crystal structures of the Met121His mutant of azurin from Alcaligenes denitrificans at pH 6.5 (1.89- and 1.91-A resolutions) and pH 3.5 (2.45-A resolution) show that the preformed metal binding cavity in the protein is more flexible than expected. At high pH (6.5), the Cu site retains the same three equatorial ligands as in the wild-type azurin and adds His121 as a fourth strong ligand, creating a tetrahedral copper site geometry with a green color referred to as 1.5 type. In the low pH (3.5) structure, the protonation of His121 causes a conformational change in residues 117-123, moving His121 away from the copper. The empty coordination site is occupied by an oxygen atom of a nitrate molecule of the buffer solution. This axial ligand is coordinated less strongly, generating a distorted tetrahedral copper geometry with a blue color and spectroscopic properties of a type-1 site. These crystal structures demonstrate that blue copper proteins are flexible enough to permit a range of movement of the Cu atom along the axial direction of the trigonal pyramid. 相似文献
49.
OBJECTIVES: To evaluate approaches to thyroid carcinoma invading the aerodigestive tract, with particular attention to well-differentiated carcinomas. STUDY DESIGN: Retrospective review of experience with thyroid carcinoma invading the aerodigestive tract over a 20-year period at a tertiary referral hospital. METHODS: The medical records of all patients with a diagnosis of thyroid cancer treated at Emory University Hospital, Atlanta, Georgia, from 1977 through 1997 were reviewed. Multiple clinical variables were analyzed including treatment, development of recurrence, and survival. Survival and time to local recurrence were determined by Kaplan-Meier analysis, and statistical comparisons were made using log-rank analysis. RESULTS: Five hundred thirty-six cases were identified; 28 patients (5.2%) were identified with invasive disease involving the aerodigestive tract. Histologic findings at the time of invasion included 15 well-differentiated (WD) carcinomas and 13 poorly differentiated (PD) carcinomas. Eight of the 28 patients (5 WD, 3 PD) underwent surgical resection of some portion of the aerodigestive tract with curative intent. Ten patients (8 WD, 2 PD) underwent incomplete resection with tumor left adjacent to aerodigestive tract structures. All patients undergoing incomplete resection developed local recurrence. Six required salvage resection, as opposed to no recurrences in WD carcinomas following complete resection (P = .01). Survival at 5 years for WD carcinomas undergoing complete resection versus initial incomplete resection was 100% versus 50%, respectively (P = .27). CONCLUSION: Review of our experience shows that complete resection of thyroid carcinoma invading the aerodigestive tract can offer prolonged palliation, improved local control, and the opportunity for cure in selected patients. 相似文献
50.
The stereochemistry of transient methyl group formation at C-3 of phosphoenolpyruvate (PEP) in the reaction catalyzed by 5-enolpyruvylshikimate 3-phosphate (EPSP) synthase has been examined using the pseudosubstrates, (E)- and (Z)-3-fluorophosphoenolpyruvate (FPEP). Kinetically stable, chiral [1H, 2H]fluoromethyl analogs of the reaction tetrahedral intermediate were isolated and subjected to decomposition and stereochemical analysis. EPSP synthase was found to catalyze the 2-re face addition of solvent-derived hydrogen to C-3 of FPEP (corresponding to the 2-si face of PEP). Comparison of these data with prior analogous work on the MurA reaction [Kim, D.H., Lees, W.J., & Walsh, C. T. (1995) J. Am. Chem. Soc. 117, 6380-6381] suggests that the two enolpyruvyl transferases share a common stereochemical course, further strengthening the mechanistic, structural, and evolutionary relationship between the two enzymes. 相似文献