全文获取类型
收费全文 | 2611篇 |
免费 | 84篇 |
国内免费 | 7篇 |
专业分类
电工技术 | 163篇 |
综合类 | 4篇 |
化学工业 | 945篇 |
金属工艺 | 79篇 |
机械仪表 | 57篇 |
建筑科学 | 74篇 |
矿业工程 | 2篇 |
能源动力 | 93篇 |
轻工业 | 293篇 |
水利工程 | 8篇 |
石油天然气 | 2篇 |
无线电 | 153篇 |
一般工业技术 | 470篇 |
冶金工业 | 87篇 |
原子能技术 | 65篇 |
自动化技术 | 207篇 |
出版年
2023年 | 10篇 |
2022年 | 35篇 |
2021年 | 57篇 |
2020年 | 34篇 |
2019年 | 35篇 |
2018年 | 49篇 |
2017年 | 46篇 |
2016年 | 64篇 |
2015年 | 38篇 |
2014年 | 87篇 |
2013年 | 159篇 |
2012年 | 120篇 |
2011年 | 177篇 |
2010年 | 108篇 |
2009年 | 150篇 |
2008年 | 146篇 |
2007年 | 134篇 |
2006年 | 103篇 |
2005年 | 115篇 |
2004年 | 101篇 |
2003年 | 92篇 |
2002年 | 89篇 |
2001年 | 61篇 |
2000年 | 46篇 |
1999年 | 44篇 |
1998年 | 38篇 |
1997年 | 48篇 |
1996年 | 49篇 |
1995年 | 30篇 |
1994年 | 44篇 |
1993年 | 32篇 |
1992年 | 30篇 |
1991年 | 17篇 |
1990年 | 22篇 |
1989年 | 21篇 |
1988年 | 15篇 |
1987年 | 20篇 |
1986年 | 30篇 |
1985年 | 26篇 |
1984年 | 25篇 |
1983年 | 19篇 |
1982年 | 23篇 |
1981年 | 8篇 |
1980年 | 14篇 |
1979年 | 11篇 |
1978年 | 13篇 |
1977年 | 9篇 |
1976年 | 15篇 |
1974年 | 11篇 |
1973年 | 10篇 |
排序方式: 共有2702条查询结果,搜索用时 15 毫秒
81.
82.
Large A‐type endosperm starch granules were isolated from near‐isogenic waxy and non‐waxy lines and low‐amylose mutant lines of bread wheat with a common genetic background. The amylose contents of A‐type starch ranged from 2.6% to 23.6%. Amylopectin was isolated by concanavalin A (Con A) precipitation from the isolated starch. The λmax (range: 532‐538 nm) and blue values at 680 nm (range: 0.026‐0.037) of the iodine‐amylopectin complex were not significantly different among the isolated amylopectins, indicating that amylopectins from non‐waxy and low‐amylose lines did not contain such long chains as amylose or extra‐long chains of amylopectin affecting iodine complex properties. Chain‐length distribution profiles measured by both high‐performance size‐exclusion chromatography (HPSEC) and high‐performance anion‐exchange chromatography (HPAEC) showed that the amylopectin structures of these lines were indistinguishable from each other. Extra‐long chains were not detected in the amylopectins by HPSEC measurement. The side‐chains measured by HPAEC were classified into four groups according to their degree of polymerization (DP), and the proportion of each group were in the following ranges: DP 6‐12, 26.5‐27.5%; DP 13‐24, 43.6‐44.1%; DP 25‐36, 13.6‐14.2%, and DP 37‐60, 11.0‐11.7%. The alleles on the Wx‐D1 locus, i.e., Wx‐D1a, Wx‐D1d, Wx‐D1f, and Wx‐D1g, responsible for granule‐bound starch synthase (GBSS I) biosynthesis had no influence on the properties of iodine‐amylopectin complex and the chain‐length distribution profiles of amylopectin. 相似文献
83.
The Fe–Si–B–P–Cu nanocrystalline alloys exhibit high saturation magnetic flux density (Bs) as well as good soft magnetic properties such as low coercivity, high effective permeability and low magnetostriction after nanocrystallization. In this paper, the Fe85Si2B8P4Cu1 alloy has been newly developed. On the viewpoint of magnetic softness, the Fe85Si2B8P4Cu1 nanocrystalline alloy reveals low core loss (W) at a commercially frequency of 50 Hz in the maximum induction (Bm) range of up to 1.75 T, and the W in the Bm range of less than 1.8 T is smaller than that of the highest-graded oriented Si-steel due to high magnetic flux density at 800 A/m (B800) of above 1.8 T and excellent magnetic softness originated from much higher Fe content and uniform nanocrystalline structure with small magnetostriction. The electrical resistivity (ρ) is relative higher than Si-steels. Thus the Fe–Si–B–P–Cu alloys are attractive for applying to magnetic parts such as motors, transducers, choke-coils and so-forth. 相似文献
84.
采用了微量润滑技术的钻削在长距或小孔径的条件下有必要对所供给的油雾和压缩空气进行最佳化分析.本文首先对切削变形与切削热分布的总能量进行了分析,并在把普通钻削过程中油雾假设为稳态可压缩绝热紊流状态的假设条件下,通过分析得到油膜厚度、气流速度、压缩空气温度和刀具平均温度等重要影响参数的相互关系.最后,给出微量润滑钻削条件下,切削过程中所需的油膜和压缩空气的最佳容量. 相似文献
85.
Akio Kishi Seiji Kuroda Tadanobu Inoue Takeshi Fukushima Hisami Yumoto 《Journal of Thermal Spray Technology》2008,17(2):228-233
A new testing procedure to evaluate the interfacial toughness of thermal-sprayed coatings has been developed. The newly designed
test specimen is a modification of the pin test with an artificially introduced weak interface, which is expected to open
up easily under tensile loading and act as a circumferential precrack along the interface between a coating and the substrate.
This configuration makes it possible to calculate the stress intensity factor K
Int at the tip of the precrack, which can be expressed as
, where σ0 is the apparent average stress, a the crack length, R the specimen radius, and F
I the geometrical correction function. Finite-element analysis was carried out to calculate the correction function F
I for various values of a/R. In the experiments, the flat surface of a pin was grit-blasted and a ring-shaped area from the periphery was covered with
carbon using a pencil and set into a mating dice. SUS316L stainless steel was plasma-sprayed onto the flat surface of the
pin and the dice. Then, tensile load was applied to the pin to break the weak interface containing the carbon and finally
the unmodified coating-substrate interface. The load required to pull out the pin was measured for various specimen parameters
such as a and R. The results indicate that the adhesion of the tested coatings can be represented by interface toughness of 1.9 ± 0.1 MPa m1/2. As a consequence, this testing procedure can be considered as a viable method to evaluate adhesion of a thermal-sprayed
coating on a substrate. 相似文献
86.
In order to obtain thermoplastic (before curing) and thermosetting (after curing) polyimides with high Tg for adhesive film, we prepared novel polyimides having phenylethynyl group in the side chain (44% of concentration of curing group) from asymmetric 2,3,3′,4′-biphenyltetracarboxylic dianhydride (a-BPDA), 3,4′-oxydianiline (3,4′-ODA) or 1,3-bis(4-aminophenoxy)benzene (1,3,4-APB) or 1,3-bis(3-aminophenoxy)benzene (1,3,3-APB), and 2,4-diamino-1-(4-phenylethynylphenoxy)benzene (mPDAp). Among three kinds of polymer, uncured polyimide of a-BPDA/1,3,4-APB; mPDAp had rather high Tg (265 °C, DMA) and thermoplasticity (E′ drop>103 at Tg). After curing reaction of phenylethynyl group, the Tg of the polyimide was increased dramatically (364 °C, DMA). The polyimide derived from 1,3,4-APB having less concentration of curing group (20%) was also prepared to improve further film flexibility and toughness. 相似文献
87.
Polyethylene reactor powders prepared under different conditions were characterized using transmission electron microscopy, 1H nuclear magnetic resonance and X-ray diffraction techniques. The molecular weight of the polyethylene reactor powders was around 1 × 105. A unique domain morphology, quite different from the usual melt- or solution-crystallized lamellar structure, was observed, independent of polymerization temperature (Tpoly). Annealing of reactor powders caused the aggregation of these crystalline domains, due to the significant molecular motion of the amorphous chains, before melting. The critical temperature was 20 °C higher than each Tpoly, and corresponded to the temperature at the active catalyst site producing the chain growth. The morphologies of powders prepared at the lower Tpoly contained smaller crystals that exhibited a constrained monoclinic form. In contrast, only usual orthorhombic crystals of larger size were found within the powder prepared at the higher Tpoly. These results suggest that the competitive processes of chain propagation and crystal growth upon polymerization may lead to unique variations of the crystalline and amorphous phases, but with similar intermediate components in the phase that connects them. 相似文献
88.
Tetsuji Yano Hayato Tateno Tetsuo Kishi Shuichi Shibata Kanae Matsuyama Takeshi Okita Shinya Miyamoto Hirohide Kofuji Munetaka Myochin 《Journal of the American Ceramic Society》2014,97(2):457-464
Surface structures of iron–phosphate glasses were examined using X‐ray photoelectron spectroscopy (XPS). Cr2O3, CoO, and Al2O3 were introduced to the glass by the replacement of a part of Fe2O3, and the simulated fission products are also added. The obtained glasses showed high chemical durabilities by MCC‐1 test. In situ high‐temperature and room‐temperature XPS measurements were conducted on the polished sample surfaces and also those after 1‐week chemical durability test. Unique trends were observed in XPS spectra on heating and after the chemical durability test, respectively. Nature of the glass surface of iron–phosphate glasses was explained from the point of view of surface energy, and the origin of high chemical durability and the effect of chromium ions were discussed based on the changes on surface composition and valence states of transition‐metal ions. 相似文献
89.
Adduct formation of 2-thenoyltrifluoroacetonato(tta) lantha-num(III), europium(III), and ytterbium(I II) with α-pheny 1 1 actic, α-methoxy phenyl acetic, salicylic, and o-methoxy benzoic acids in chloroform has been studied by solvent extraction technique. It has been found that 1anthanoid(111) chelates form more stable adducts with these carboxylic acids in the sequence: Yb(tta)3 < Eu(tta) 3 < La(tta) 3. The adduct formation constants as well as the separation factors obtained as the ratio of the constants between a pair of metals are the largest for α-phenyl lactic acid among these acids. The characteristics with α-phenyl 1actic acid would be caused by the action as bidentate unlike benzoic acid derivatives which work as monodentates owing to the internal complexa-tion through hydrogen bonding. 相似文献
90.
Cationic chitosan (CT) and anionic dextran sulfate (Dex) were layer-by-layer (LbL) assembled from aqueous solutions containing
1 M NaCl on a quartz crystal microbalance (QCM) substrate, and the original films ((CT-Dex)3-CT)) were end-capped with LbL assembly from CT solutions containing 1 M NaCl and Dex solutions without NaCl. The enzymatic
degradation of films by chitosanase was quantitatively analyzed by QCM in terms of numbers of end-capping steps. The degradation
of films end-capped with (Dex-CT)3 was considerably prolonged when compared to those end-capped with other end-capping steps. A mechanism for the prolonged
degradation was proposed by quantitative QCM data and zeta potential results. 相似文献