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51.
Donald B. Parrish Jack C. Bauernfeind 《Critical reviews in food science and nutrition》1977,9(4):375-394
Formerly, few foods were routinely analyzed for vitamin A, but recent emphasis on nutrient requirements, nutrient labeling, and use of dietary convenience foods has created need for determining vitamin A in a variety of foods. There are many vitamin A methods — some suitable for certain products only. For regulatory purposes, the FDA specifies the AOAC method where it is applicable. However, some food analysts and organizations continue with their own vitamin A methods. If possible, a single, widely applicable general method should be used for vitamin A in foods. Vitamin A may be determined by spectrophotometric, colorimetric, and fluorometric procedures. Sometimes chromatography is required as an important part of the method. Colorimetric procedures with SbCl3 are now most widely used to measure vitamin A (retinol) in foods. If vitamin A content is high enough and extracts sufficiently free of interfering substances, spectrophotometric or flurometric methods are satisfactory. Methods in various stages of development for determining vitamin A in foods are based on flurospectrophotometry, gas‐liquid chromatography, high‐performance liquid chromatography, and automation. To estimate total vitamin A nutritional value of certain foods may also require determination of vitamin A isomerization and contents of carotenes, cryptoxanthin, reinaldehyde, and apo‐carotenal. 相似文献
52.
I. Marta Evans Donald Boulter Robert L. Fox B. T. Kang 《Journal of the science of food and agriculture》1977,28(2):161-166
Seed meals of three cowpea (Vigna unguiculata) cultivars, grown in pots containing sulphur-deficient soil supplemented with 0, 0.2, 0.6, 1.8, 5, 15 and 45 parts/106 sulphate-S levels in the soil solution, were examined for total nitrogen, total sulphur and sulpho-amino acid contents. The sulphur content and the ratio of sulphur to nitrogen were found to increase with the increasing level of sulphate-S fertilisation up to ca 5 parts/106. Compared with the control the sulpho-amino acid content in seeds of cowpea TVu 76 increased with S-supplementation up to 5 parts/106 and that of cowpea Sitao Pole increased with S up to 1.8 parts/106. Similar levels (7 and 2 parts/106 respectively) of sulphate-S were required in the soil solution to obtain 95% of the maximum yields of cowpea seeds. The content of sulpho-amino acids in the seeds from 5 parts/106 treatments were similar to those reported for cowpeas grown under field conditions at IITA and elsewhere with adequate levels of soil sulphur for maximum yield. 相似文献
53.
Mozar Naing Dallas Webster Nolan Blue Rick Hudgens Zahir Parkar Sumeer Bhatara Pankaj Gupta Donald Y. C. Lie 《Journal of Electronic Testing》2012,28(5):723-731
High volume production environments create great challenges for production testing and verification of Radio Frequency (RF) devices. In this environment, much emphasis is put on parallel testing, or the ability to test multiple devices at the same time using a single tester. In order for this parallelism to become a reality, there is a need for production RF tests to be simplified and reduced to requiring only the simplest test stimulus and analysis. In this paper, we present a new method of measuring the performance of a Frequency Modulation (FM) receiver that requires only a continuous wave signal input in order to eliminate the more costly Signal-to-Noise Ratio test. Using this new technique we will then demonstrate how simplifying this test and adding frequency diversity enables testing of up to 8 devices in parallel using a single tester. 相似文献
54.
Donald E. Johnston Denise Kelly Pauline P. Dorrian 《Journal of the science of food and agriculture》1983,34(7):733-736
Differences in the extent of loss of pectic substances from potato (Solanum tuberosum L.) after boiling, steaming and pressure cooking were investigated. Losses were found to be significantly greater (P< 0.001) after boiling than after pressure cooking or steaming. The pectic substance content (g 100 g?1 dry matter) of potatoes (cv. Pentland Crown) was 2.98 for raw peeled tubers, 0.97 after boiling for 35 min, 1.22 after steaming for 35 min and 1.24 after pressure cooking at 103.4 kPa (15 psi) for 15 min. The roles of cooking time, cooking temperature and heat transfer medium are discussed. The effects of calcium sulphate (at levels typical of ‘hard’ and ‘soft’ water supplies) in the cooking water on losses of pectic substances from potato (Solanum tuberosum L.), carrot (Daucus carota L.), and swede (Brassica napus L. var. napobrassica Peterm.) after boiling and pressure cooking were also investigated. Water hardness did not influence losses during pressure cooking but samples boiled in hard water had decreased losses of pectic substances compared to those boiled in soft water. The increase in retention of pectic substances due to hard water was about 8 % for potatoes (cv. Pentland Dell), about 33 % for sliced carrots (cv. Berlicum, approved maintenance Perfecta) and about 23% for diced swedes (cv. Acme). The interaction of water hardness with cooking method was significant for potato (P< 0.05) and swede (P<0.001) and approaching significance (P=0.055) for carrot. 相似文献
55.
Ytterbium trialuminide (YbAl3) has one of the largest thermoelectric power factors of known materials below room temperature, making it a material of interest for low-temperature thermoelectric devices. However, the high thermal conductivity, which is due to a combination of a large electronic thermal conductivity and a moderately large lattice thermal conductivity, is detrimental to the figure of merit. Substitution of different atoms on the Yb site was performed in order to assess their ability to favorably alter the electronic structure and/or reduce the lattice thermal conductivity. We have synthesized and studied the thermoelectric properties of the solid solutions of YbAl3 with ErAl3 and LuAl3. Results for electrical conductivity, thermal conductivity, and Seebeck coefficient for several of these solid solutions over the temperature range of 80 K to 300 K are reported. Although most substituted samples are driven toward a metallic state, we find that for some compositions the figure of merit is enhanced relative to pure YbAl3. 相似文献
56.
57.
Donald Schelle 《电子设计技术》2007,14(3):120-120,124
USB端口为辅助设备提供方便的5V电源.USB端口不仅向微控制器和其它基本电路供电,而且还提供足够的额外电流净空来给小电池或超级电容器储能元件充电. 相似文献
58.
Ashok K. Sood James E. Egerton Yash R. Puri Enrico Bellotti Donald D’Orsogna Latika Becker Raymond Balcerak Ken Freyvogel Robert Richwine 《Journal of Electronic Materials》2005,34(6):909-912
Multicolor infrared (IR) focal planes are required for high-performance sensor applications. These sensors will require multicolor
focal plane arrays (FPAs) that will cover various wavelengths of interest in mid wavelength infrared/long wavelength infrared
(MWIR/LWIR) and long wavelength infrared/very long wavelength infrared (LWIR/VLWIR) bands. There has been significant progress
in HgCdTe detector technology for multicolor MWIR/LWIR and LWIR/VLWIR FPAs.1–3 Two-color IR FPAs eliminate the complexity of multiple single-color IR FPAs and provide a significant reduction of weight
and power in simpler, reliable, and affordable systems. The complexity of a multicolor IR detector MWIR/LWIR makes the device
optimization by trial and error not only impractical but also merely impossible. Too many different geometrical and physical
variables need to be considered at the same time. Additionally, material characteristics are only relatively controllable
and depend on the process repeatability. In this context, the ability of performing “simulation experiments” where only one
or a few parameters are carefully controlled is paramount for a quantum improvement of a new generation of multicolor detectors
for various applications. 相似文献
59.
John P. Ranieri Frederick S. Lauten Donald H. Avery 《Journal of Electronic Materials》1995,24(10):1419-1423
The aspect ratio (joint area/joint thickness) of thin (0.001-0.006 in.) surface mount solder (60S-40Pb) joints plays an important
role in determining the mechanical properties and fracture behavior of the joints. This study demon-strates that plastic constraint
of a large aspect ratio 60Sn-40Pb solder joint can develop triaxial (hydrostatic) stresses several times greater than the
average tensile strength of the bulk solder material. A four to sixfold increase in average joint stress and up to a tenfold
increase in peak stress was measured on joints with aspect ratios ranging from 400 to 1000. Although a direct relationship
of the aspect ratio to the average tensile stress is shown, as the Friction Hill model predicts, the observed stress increase
is not nearly as high but proportional to the classical prediction. This is attributed to the existence of internal defects
(oxide particles and micro-voids) and transverse grain boundaries which fail producing internal free surfaces. Thus, the actual
aspect ratio is thickness/d2, where d equals the distance between internal surfaces. The fracture of these constrained joints was brittle, with the separation
occurring between a tin-rich copper tin intermetallic at the interface and the solder matrix. Voids within the solder joint
are shown to relieve the plastic constraint and lower the average tensile stress of the joint. The Friction Hill model may
play an important role in explaining the small percentage of atypical solder joint failures which sometimes occur on electronic
assemblies. In particular, the sudden failure of a thin joint in a strain controlled environment may be attributed to the
development of a large hydrostatic stress component. Therefore, a flaw free, plastically constrained joint which develops
a high stress state will be a high risk candidate for failure. 相似文献
60.
现代通信系统电源设计 总被引:1,自引:0,他引:1
DonaldAshley 《今日电子》2004,(12):62-64
通信设备使用的电源器件有很多种,从前端的功率因数校正(PFC)AC/DC电源到后端的高效DC/DC模块和负载点(POL)转换器,不一而足。从需要很高效率的中间总线转换器(IBC),到那些日趋细小轻巧的VoIP数字电话,以及要求多路紧密调节电压(7~13路输出)的数字用户线(xDSL)电源等,DC/DC电源在现代通信中获得了广泛应用。 相似文献