全文获取类型
收费全文 | 742篇 |
免费 | 17篇 |
国内免费 | 10篇 |
专业分类
化学 | 570篇 |
晶体学 | 16篇 |
力学 | 4篇 |
数学 | 105篇 |
物理学 | 74篇 |
出版年
2023年 | 2篇 |
2022年 | 2篇 |
2021年 | 9篇 |
2020年 | 6篇 |
2019年 | 16篇 |
2018年 | 5篇 |
2017年 | 11篇 |
2016年 | 14篇 |
2015年 | 6篇 |
2014年 | 22篇 |
2013年 | 32篇 |
2012年 | 44篇 |
2011年 | 55篇 |
2010年 | 23篇 |
2009年 | 31篇 |
2008年 | 40篇 |
2007年 | 40篇 |
2006年 | 45篇 |
2005年 | 42篇 |
2004年 | 48篇 |
2003年 | 38篇 |
2002年 | 32篇 |
2001年 | 17篇 |
2000年 | 17篇 |
1999年 | 3篇 |
1998年 | 15篇 |
1997年 | 14篇 |
1996年 | 13篇 |
1995年 | 3篇 |
1994年 | 5篇 |
1993年 | 6篇 |
1992年 | 4篇 |
1991年 | 6篇 |
1990年 | 8篇 |
1989年 | 11篇 |
1988年 | 7篇 |
1987年 | 3篇 |
1986年 | 4篇 |
1985年 | 8篇 |
1984年 | 11篇 |
1983年 | 7篇 |
1982年 | 7篇 |
1981年 | 4篇 |
1980年 | 6篇 |
1979年 | 5篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1975年 | 7篇 |
1974年 | 3篇 |
1939年 | 1篇 |
排序方式: 共有769条查询结果,搜索用时 156 毫秒
91.
92.
Masakazu Yoshikawa Hideto Yokoi Kohei Sanui Naoya Ogata 《Journal of polymer science. Part A, Polymer chemistry》1984,22(9):2159-2168
Separation of various alcohols and water through a membrane was carried out by means of a hydrogen-bonding interaction. A membrane obtained from poly(maleimide-co-acrylonitrile) was effective for a selective separation of water from aqueous alcohol solution by pervaporation technique. Spectroscopic analyses verified that this high selectivity was attributed to the hydrogen-bonding interaction between water and maleimide units in the membrane. 相似文献
93.
The structures of neopeptins A (1), B (2), and C (3) were elucidated on the basis of chemical and spectroscopic evidences. 相似文献
94.
Tu-zhu-ye is a Korean crude drug for use as a diuretic but its plant source has not been identified. The present work has been attempted for identification of the original plant using specimens collected both at Seoul and Taegu, Korea, their mineral microstructures being examined after ashing the specimens by a low-temperature method with high-frequency oxygen plasma. A preliminary survey of the specimens with the naked eye suggested that the Tu-zhu-ye was near to Phyllostachys or its closely related bamboo species. Several specimens, namely, Phyllostachys heterocyclaMitf. var. pubescensOhwi, Phyllostachys nigraMunro var. henonisStapf, Phyllostachys bambusoidesSieb. et Zucc. and Bambusa multiplexRaeuschel were therefore ashed by the low-temperature method and the comparative microscopic studies with the resultant ashed tissues concluded that the “Tu-zhu-ye” from Seoul was perfectly identical with Phyllostachys nigraMunro var. henonisStapf. A further investigation is continued for the specimen from Taegu since it is different from any other specimens provided for the present work. 相似文献
95.
Masakazu Ichiyanagi 《Physics letters. A》1980,79(1):95-97
With a plausible assumption for ψ(r), a bubble-solution of the GP-equation in the three-dimensional case is obtained. The relation between a roton and a “bubble” is examined. The roton spectrum is derived in order to test the suggested theory of condensate wavefunctions. 相似文献
96.
Susumu Nakashima Masakazu Yagi Michio Zenki Akinori Takahashi Kyoji Tôei 《Fresenius' Journal of Analytical Chemistry》1984,319(5):506-509
Summary Nitrate was determined in natural water samples by flow-injection spectrophotometry. It was reduced to nitrite with copperized cadmium and the nitrite thus produced reacted with p-aminoacetophenone and m-phenylenediamine. The limit of detection was about 1.5 g l–1 for sample injections of 650 l. The sampling rate was about 40 samples h–1 and the relative standard deviation was above 1% for 0.1–0.3 mg l–1 nitratenitrogen. Nitrite present in the sample was determined separately and subtracted.
Nitratbestimmung in natürlichen Wässern mit Hilfe der Fließinjektions-Analyse
Zusammenfassung Nitrat wird bei dieser Methode mit Hilfe einer Cu/Cd-Reduktionssäule zu Nitrit reduziert, das mit p-Aminoacetophenon und m-Phenylendiamin zur Reaktion gebracht wird. Die gebildete Verbindung wird spektral-photometrisch gemessen. Die Nachweisgrenze beträgt etwa 1,5 g/l bei injizierten Probevolumina von 650 l. Der Probendurchsatz beträgt 40/h. Die relative Standardabweichung liegt über 1% bei 0,1–0,3 mg/l Nitrat-Stickstoff. Vorhandenes Nitrit wird gesondert bestimmt und abgezogen.相似文献
97.
Domino Michael reactions of oxophorone and its derivatives 4 with Michael partners 3 have been effected to give bicyclo[2.2.2]octane-2,5-dione derivatives 7 by a catalytic amount of a Brønsted base (NMAP-Li) generated from N-methylaminopropylated silica gel (NMAP) and n-BuLi. The NMAP pellets were efficiently reused up to six times in 86% average yield. 相似文献
98.
99.
Representation of a given nonnegative multivariate polynomial in terms of a sum of squares of polynomials has become an essential subject in recent developments of sums of squares optimization and semidefinite programming (SDP) relaxation of polynomial optimization problems. We discuss effective methods to obtain a simpler representation of a sparse polynomial as a sum of squares of sparse polynomials by eliminating redundancy.A considerable part of this work was conducted while this author was visiting Tokyo Institute of Technology. Research supported by Kosef R004-000-2001-00200Mathematics Subject Classification (1991): 90C22, 90C26, 90C30 相似文献
100.
Susumu Nakashima Masakazu Yagi Michio Zenki Mitsuo Doi Kyoji Tôei 《Fresenius' Journal of Analytical Chemistry》1984,317(1):29-31
Summary Sulphate was determined in natural water samples by flow-injection analysis using dimethylsulphonazo-III as reagent. The interference by Ca was eliminated by a cation-exchanger column inserted directly after the sample injection valve. In order to ensure high sensitivity and reproducibility it was necessary to saturate the carrier solution with barium sulphate and to fill the reaction coil with ethanol-water (11) when not in use. Standard deviations were 0.94–1.2% for 6–10mg/l sulphate. The limit of detection was about 0.2mg/l. The calibration graph was linear up to 14mg/l Mg2+, NH
4
+
, Na+, K+, Cl–, NO
3
–
, PO
4
3–
, HCO
3
–
and SiO
3
2–
did not interfere in the normally occurring concentrations.
Sulfatbestimmung in natürlichem Wasser durch Flow-Injection-Analyse
Zusammenfassung Als Reagens dient Dimethylsulfonazo-III. Die Störung durch Calcium bei dieser Bestimmung wird durch eine Kationenaustauschersäule eliminiert, die direkt nach dem Probeinjektions-Ventil angeordnet ist. Zur Erhöhung der Empfindlichkeit und Reproduzierbarkeit ist es notwendig, die Trägerlösung mit Bariumsulfat zu sättigen sowie bei Nichtbenutzung des Systems den Reaktionsteil mit Ethanol-Wasser (11) zu füllen. Mit dem so modifizierten Verfahren ergaben sich Standardabweichungen von 0,94–1,2% für 6–10 mg/l Sulfat, die Nachweisgrenze liegt bei 0,2 mg/l. Die Eichkurve ist bis 14 mg/l linear. Mg2+, NH 4 + , Na+, K+, Cl–, NO 3 – , PO 4 3– , HCO 3 – und SiO 3 2– stören in den normalerweise vorkommenden Konzentrationen nicht.相似文献