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41.
This paper presents a mathematical review of methods and algorithms used to compute milling cutter placement for multi-axis finished-surface machining. In general, these methods and algorithms compute tool path points based on tangent-plane contact between the milling cutter and the surface while maintaining a fixed tool orientation. This tangent-plane method of tool positioning and orientation is examined by discussing its strengths and weaknesses. Errors resulting from the tangent-plane approach are typically determined using a posteriori cutter path checking and graphic visualization techniques. Although these checking techniques have proved useful in identifying the tool path errors before actual machining, the problem of generating an error-free tool path remains. In this paper, we discuss the analysis of tool path position and orientation data as they are generated. This a priori analysis method is used to show error locations along the lateral face of the tool. The conclusion is reached that additional research is needed in the area of simultaneous multi-axis tool path planning, if errors are to be eliminated and the efficiency of the milling machine is to be improved. The reader is referred to research efforts that extend beyond the traditional or computer-aided design (CAD, vendor supplied) tool path planning methods. Some of these efforts show great promise in eliminating gouging and improves machine tool efficiency. 相似文献
42.
Although the banking industry plays a central role in the world economy and has traditionally been an innovative user of information technology, banks are struggling to develop mature Internet strategies. A model used to analyze the type of Internet activities among a sample of banks as well as their level of sophistication and customization is useful not only for revealing unexploited opportunities in the banking sector but also for guiding the strategy-building process of organizations in other industries. 相似文献
43.
44.
The objective of this investigation was to demonstrate that the firmness of a commercial vegetable product, diced and frozen red pepper (Capsicum annum var. Sendt), could be improved by the use of exogenous pectinesterase in an industrially relevant process. The diced pepper pieces 10 × 10 × 7 mm3 were infused under vacuum with a commercially available pectinesterase. The range of optimal process conditions was: 15-20°C, 45 min infusion time, a 10-25 mM CaCl2 infusion brine, a w/w ratio of pepper fruit to infusion brine of 1.5:1, and an enzyme dosage of 30-60 pectinesterase units (PEU) per kg pepper fruit. The firmness as measured by back extrusion was improved by a factor of two to three. The effect of firming was robust and conserved after freezing and heating in a simulated household cooking process. The firming process seems easily adaptable to industrial conditions and may be applicable to other vegetable and fruit products. 相似文献
45.
Efficient scheduling systems are able to enhance production flow and production times in process industry. Scheduling, in this case, means simulation with alternatives of resources and/or activities. The result will be the exact time of output for each activity and the resulting profiles of capacity vectors concerning the recommended resources. In contrast to this, common planning systems add only the user defined production time of activities. Especially for flexible plants with batch production and a variable spectrum of products, as weil as for plants in the stage of design or enlargement, scheduling systems can be very helpful in identifying bottlenecks and over-capacities. Therefore, reduction of costs in a significant extent and additional benefits can be realized, provided that the individual conditions and objectives have been taken into account. 相似文献
46.
Localization of putative tumor suppressor loci by genome-wide allelotyping in human pancreatic endocrine tumors 总被引:1,自引:0,他引:1
DC Chung SB Brown F Graeme-Cook LG Tillotson AL Warshaw RT Jensen A Arnold 《Canadian Metallurgical Quarterly》1998,58(16):3706-3711
Only two tumor suppressor gene loci, one on 3p25 and the MEN1 gene on 11q13, have thus far been implicated in the pathogenesis of sporadic human pancreatic endocrine tumors (PETs). A genome-wide allelotyping study of 28 human PETs was undertaken to identify other potential tumor suppressor gene loci. In addition to those on chromosomes 3p and 11q, frequent allelic deletions were identified on 3q (32%), 11p (36%), 16p (36%), and 22q (29%). Finer deletion mapping studies localized the smallest regions of common deletion to 3q27, 11p13, and 16p12.3-13.11. Potential candidate genes at these loci include WT1 (11p13), TSC2 (16p13), and NF2 (22q12), but no known tumor suppressor gene localizes to 3q27. The mean fractional allelic loss among these human PETs is 0.126, and no correlation was observed between allelic loss and clinical parameters, including age, sex, hormonal subtype, and disease stage. These findings highlight novel locations of tumor suppressor gene loci that contribute to the pathogenesis of human PETs, and several of these on 3p, 3q, and 22q are syntenic with loci on mouse chromosomes 9 and 16 that are implicated in a murine transgenic model of PETs. 相似文献
47.
Asendorpf Jens B.; Warkentin Veronique; Baudonnière Pierre-Marie 《Canadian Metallurgical Quarterly》1996,32(2):313
Eighteen-month-old children were tested for mirror self-recognition using the classic rouge test or an alternative procedure, for social contingency awareness by being closely imitated for a long time, and for the capacity for communication by synchronic imitation. The classic mirror rouge test was shown to produce false negatives. Most recognizers and nonrecognizers became aware of being imitated and imitated the activity of a model, but only recognizers engaged in sustained synchronic imitation of the model. The results support our hypothesis that self-recognition and spontaneous perspective-taking develop in close synchrony because both require a capacity for secondary representation. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
48.
A dilatometer for measuring autogenous deformation in hardening portland cement paste 总被引:1,自引:1,他引:0
Different techniques for measuring autogenous deformation in cement paste are discussed, and a newly developed dilatometer designed specially for measuring this deformation is described. A particular characteristic of the dilatometer is the encapsulation of the cement paste in corrugated moulds. This restricts moisture loss and ensures that the hardening cement paste suffers insignificant restraint. In addition, the encapsulation permits measurements to commence shortly after casting. 相似文献
49.
Henning H. Mikkelsen Jens Oddershede John R. Sabin Ejvind Bonderup 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》1995,100(4):451-457
We derive a Bethe formula for the stopping of swift ions by target molecules oriented with respect to the beam. The theory is characterized by a directional mean excitation energy formed from transition energies and dipole matrix elements. The expression for the mean excitation energy is similar to the one for an isotropic sample but the dipole matrix elements corresponding to the various transition moment directions carry unequal weights which depend on the orientation of the molecule with respect to the beam. For a large class of molecules, the logarithm of the mean excitation energy is linear in sin2 θ, where θ denotes the angle between the beam and the principal molecular axis. We illustrate the properties of the theory in the simple case of a diatomic molecule. 相似文献
50.
BB Kragelund P H?jrup MS Jensen CK Schjerling E Juul J Knudsen FM Poulsen 《Canadian Metallurgical Quarterly》1996,256(1):187-200
Bovine acyl-coenzyme A binding protein is a four-helix bundle protein belonging to a group of homologous eukaryote proteins that binds medium and long-chain acyl-coenzyme A esters with a very high affinity. The three-dimensional structure of both the free and the ligated protein together with the folding kinetics have been described in detail for the bovine protein and with four new sequences reported here, a total of 16 closely related sequences ranging from yeasts and plants to human are known. The kinetics of folding and unfolding in different concentrations of guanidine hydrochloride together with equilibrium unfolding have been measured for bovine, rat and yeast acyl-coenzyme A binding protein. The bovine and rat sequences are closely related whereas the yeast is more distantly related to these. In addition to the three natural variants, kinetics of a bovine mutant protein, Tyr31 --> Asn, have been studied. Both the folding and unfolding rates in water of the yeast protein are 15 times faster than those of bovine. The folding rates in water of the two mammalian forms, rat and bovine, are similar, though still significantly different. A faster unfolding rate both for rat and the bovine mutant protein results from a lower stability of the native states of these. These hydrophobic regions, mini cores, have been identified in the three-dimensional structure of the bovine protein and found to be formed primarily by residues that have been conserved throughout the entire eukaryote evolution from yeasts to both plants and mammals as seen in the sample of 16 sequences. The conserved residues are found to stabilize helix-helix interactions and serve specific functional purposes for ligand binding. The fast one-step folding mechanism of ACBP has been shown to be a feature that seems to be maintained throughout evolution despite numerous differences in sequence and even dramatic differences in folding kinetics and protein stability. The protein study raises the question to what extent does the conserved hydrophobic residues provide a scaffold for an efficient one-step folding mechanism. 相似文献