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排序方式: 共有1307条查询结果,搜索用时 15 毫秒
21.
Phani Kumar V. V. Nukala William Shelton Jr 《International journal for numerical methods in engineering》2007,69(12):2636-2662
This paper presents two semi‐implicit algorithms based on splitting methodology for rigid body rotational dynamics. The first algorithm is a variation of partitioned Runge–Kutta (PRK) methodology that can be formulated as a splitting method. The second algorithm is akin to a multiple time stepping scheme and is based on modified Crouch–Grossman (MCG) methodology, which can also be expressed as a splitting algorithm. These algorithms are second‐order accurate and time‐reversible; however, they are not Poisson integrators, i.e. non‐symplectic. These algorithms conserve some of the first integrals of motion, but some others are not conserved; however, the fluctuations in these invariants are bounded over exponentially long time intervals. These algorithms exhibit excellent long‐term behaviour because of their reversibility property and their (approximate) Poisson structure preserving property. The numerical results indicate that the proposed algorithms exhibit superior performance compared to some of the currently well known algorithms such as the Simo–Wong algorithm, Newmark algorithm, discrete Moser–Veselov algorithm, Lewis–Simo algorithm, and the LIEMID[EA] algorithm. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
22.
State laws on youth access to tobacco in the United States: measuring their extensiveness with a new rating system 总被引:1,自引:0,他引:1
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Alciati MH Frosh M Green SB Brownson RC Fisher PH Hobart R Roman A Sciandra RC Shelton DM 《Tobacco control》1998,7(4):345-352
OBJECTIVE: To develop and implement a rating system evaluating the extensiveness of state laws restricting youth access to tobacco. DESIGN: State laws on youth access to tobacco were analysed and assigned ratings on nine items. Six items addressed specific tobacco-control provisions, and three related to enforcement provisions. For each item, a target was specified reflecting public health objectives. Achieving the target resulted in a rating of +4 points; for three items, a rating of +5 was possible if the target was exceeded. Criteria for lower ratings were established for situations when the target was not met. SETTING: United States. RESULTS: State scores (sum of the ratings across all nine items) ranged from 0-18 in 1993, 2-21 in 1994, and 1-21 in 1995 and 1996, out of a possible total of 39. The average score across states was 7.2 in 1993, 7.9 in 1994, 8.2 in 1995, and 9.0 in 1996. The overall mean rating (per item) was 0.80 in 1993, 0.88 in 1994, 0.91 in 1995, and 1.00 in 1996, on a scale where 4.0 indicates that the target goals (per item) were met. From 1993 to 1996, scores increased for 20 states, decreased for one state, and remained unchanged for the others. The number of states for which state preemption of local tobacco regulation was a factor doubled from 10 states in 1993 to 20 states in 1996. CONCLUSIONS: Although all states have laws addressing youth access to tobacco, this analysis reveals that, as of the end of 1996, the progress towards meeting health policy targets is slow, and state legislation that preempts local tobacco regulation is becoming more common. 相似文献
23.
24.
This paper presents the design, performance, and operational characteristics of a new direct reading instrument for determining nitrogen in cereal and grain. Precision, accuracy, range, speed, ease of operation, sensitivity, sample size, and flexibility of the instrument are presented. Results on various cereals and grains are presented and compared with those obtained by the Kjeldahl technique. The apparatus is the result of research for a rapid method for determining nitrogen in organic material. The instrument uses a combination of a unique high temperature sample oxidation, a sampling valve for separating combustion products, and thermal conductivity detection for the liberated nitrogen in a helium carrier gas. 相似文献
25.
Brett E. Shelton Jennifer Turns Tracey S. Wagner 《Behaviour & Information Technology》2002,21(3):209-222
This study followed the introduction of the Arthritis Source website into the existing teaching practices of Arthritis Foundation Helpline volunteers. The goal was to examine what factors may affect a particular group of educators adopt a potentially valuable Internet tool into an existing instructional environment. Defining the possible uses of the website in reference to the volunteers' actual job duties helped provide a clearer understanding of how the volunteers might use this new technology. The researchers used qualitative techniques to focus on three volunteers who experienced different physical, environmental and cognitive means that impacted their use of the new tool. Each volunteer experienced varying levels of motivation in areas of learning, satisfaction and responses to outside influences. Each volunteer also had varying amounts of opportunity prompts in which to interact or refer the website. Consequently, Helpline volunteers experienced different rates of adopting the information-intensive website into their traditional work system. 相似文献
26.
S Djurickovic RN Meek CF Snelling HM Broekhuyse PA Blachut PJ O'Brien JC Boyle 《Canadian Metallurgical Quarterly》1996,41(5):825-830
OBJECTIVE: To review the results of surgical management of heterotopic ossification about the elbow in burned patients. DESIGN: Retrospective analysis with long-term patient follow-up. MATERIALS AND METHODS: Eleven patients with 16 elbows requiring surgery were admitted between January 1, 1982 and December 31, 1993. A posterior approach to the elbow with release of the encased ulnar nerve +/- anterior transposition and transolecranon osteotomy to access extensive bone formation in the olecranon fossa was employed. Eight patients (11 elbows) were available for long-term follow-up conducted at mean 50 +/- 13 months after surgery. Long-term follow-up consisted of measurement of range of elbow motion, as well as clinical assessment of ulnar nerve function. MAIN RESULTS: For the 11 elbows examined postoperatively, the mean range of motion preoperatively in flexion-extension was 11 degrees +/- 5 degrees compared to 89 degrees +/- 12 degrees postoperatively (p < 0.001). Three patients with poor long-term results had ankylosis of the joint preoperatively. Of four patients with ulnar nerve paresis preoperatively, none had ulnar nerve dysfunction at follow-up. Of 16 elbows operated on, four (25%) had postoperative complications. Two suffered soft-tissue breakdown with hardware exposure requiring abdominal flap closure, one early failure of olecranon fixation, and one late infected hardware. CONCLUSIONS: Surgery for both limited range of motion as well as ulnar nerve compression is effective in cases of heterotopic ossification about the elbows of burned patients. Early operative intervention is indicated in progressive disease, particularly ulnar nerve palsy, if soft-tissue quality is adequate. Complications with 25% of elbows suggest that use of olecranon osteotomy for joint access may warrant review. 相似文献
27.
An innovative model for organising social services in a community, the Imbrication Model, is contrasted with two traditional models, the Entrepreneurial and the Umbrella Agency. The structural characteristics and dynamics of the three models are illustrated with actual case histories. Imbrication Model calls for the interlocking of personnel from several agencies, with the purpose of redirecting the dysfunctional interagency rivalry prevalent in the traditional models. Imbrications at all organisational levels--Board of Directors, Administrators and Staff--facilitate adoption of the superordinate goal of providing clients with the best services available, regardless of which particular agency delivers the service. Few observers of the current social service scene would challenge the statement that needs for service are unlimited and resources limited. In the USA the imbalance between needs and resources persists despite a decade of massive governmental programmes intended to alleviate social ills. Recent substantial cutbacks in federal funds, moreover are not likely to improve the situation. The resource shortage involves more than a limitation of funds. Deliverers of service and competent programme administrators are also on critically short supply. These shortages are more often than not exacerbated by a chronic spirit of competition among agencies and programmes at the local level. Three organizational models for the delivery and administration of social services, two conventional and one of more recent date, are examined in this article. The innovative model, which has been named the Imbrication Model, explicitly calls for redirecting interagency rivalry and competition. Its ambitious goal is to integrate the efforts of those attempting to meet a community's social service needs. 相似文献
28.
Primary bone-derived cell colonization of unconditioned and pre-conditioned Bioglass 45S5 surfaces in vitro 总被引:1,自引:0,他引:1
Samples of Bioglass 45S5, a bioactive glass that reacts chemically on immersion in an aqueous environment and following implantation can bond with bone, were immersed in culture medium with foetal calf serum as a source of proteins for periods of 1–11 days. Energy dispersive spectroscopy (EDS) revealed that over 11 days immersion, the Bioglass surface was rich in Si relative to Ca and P and scanning electron microscopy (SEM) showed that the Bioglass developed surface reaction layers. Samples conditioned in culture medium and previously untreated samples were used as substrates for primary osteoblast or periosteal cell cultures, to allow comparison of the effects of different Bioglass surface development, on subsequent cell attachment. SEM examination revealed that pre-conditioned Bioglass was a more suitable substrate for osteoblast colonization than previously undeveloped Bioglass, whereas periosteal cells colonized all samples equally well and more rapidly than osteoblasts. 相似文献
29.
30.
Magnetic measurements have been performed on single crystals of TlBa
2
Ca
3
Cu
4
O
11+
in the magnetic fields up to 5.5 T. No change in the onset temperature of superconducting transition (T
c
) was observed in the magnetic fields between 0.4 and 5.5 T, while the superconducting transitions were broadened significantly in the same field. The linear temperature-dependence of the magnetization was found in a large temperature range below T
c
. The slope of the magnetization versus temperature
decreased significantly with increasing magnetic field. The experimental findings indicated that the upper critical field (H
C2
) in this compound was very large and traditional methods of deriving H
C2
value were not applicable. Using the measured magnetization in the reversible region, the H
C2
properties of TlBa
2
Ca
3
Cu
4
O
11+
single crystals have been studied based on a new model developed by Hao et al. 相似文献