全文获取类型
收费全文 | 3618篇 |
免费 | 132篇 |
国内免费 | 7篇 |
专业分类
电工技术 | 52篇 |
综合类 | 4篇 |
化学工业 | 582篇 |
金属工艺 | 88篇 |
机械仪表 | 62篇 |
建筑科学 | 116篇 |
矿业工程 | 10篇 |
能源动力 | 86篇 |
轻工业 | 231篇 |
水利工程 | 27篇 |
石油天然气 | 13篇 |
无线电 | 382篇 |
一般工业技术 | 496篇 |
冶金工业 | 1209篇 |
原子能技术 | 31篇 |
自动化技术 | 368篇 |
出版年
2022年 | 33篇 |
2021年 | 32篇 |
2020年 | 25篇 |
2019年 | 43篇 |
2018年 | 52篇 |
2017年 | 45篇 |
2016年 | 55篇 |
2015年 | 50篇 |
2014年 | 68篇 |
2013年 | 144篇 |
2012年 | 78篇 |
2011年 | 121篇 |
2010年 | 73篇 |
2009年 | 101篇 |
2008年 | 108篇 |
2007年 | 111篇 |
2006年 | 82篇 |
2005年 | 69篇 |
2004年 | 72篇 |
2003年 | 62篇 |
2002年 | 87篇 |
2001年 | 68篇 |
2000年 | 45篇 |
1999年 | 74篇 |
1998年 | 353篇 |
1997年 | 232篇 |
1996年 | 132篇 |
1995年 | 114篇 |
1994年 | 88篇 |
1993年 | 91篇 |
1992年 | 60篇 |
1991年 | 34篇 |
1990年 | 44篇 |
1989年 | 40篇 |
1988年 | 58篇 |
1987年 | 65篇 |
1986年 | 39篇 |
1985年 | 51篇 |
1984年 | 49篇 |
1983年 | 46篇 |
1982年 | 47篇 |
1981年 | 37篇 |
1980年 | 40篇 |
1979年 | 24篇 |
1978年 | 24篇 |
1977年 | 36篇 |
1976年 | 79篇 |
1974年 | 32篇 |
1973年 | 34篇 |
1969年 | 23篇 |
排序方式: 共有3757条查询结果,搜索用时 31 毫秒
51.
Pretreatment of murine leukaemia L1210 cells with non-lethal concentrations of various antimetabolites increased the in vitro invasive capacity of these cells into monolayers of rat embryo fibroblasts. The increase in invasive capacity was partly correlated with the induced cell cycle arrest. The concomitant increase in cell surface fucosylation and inhibition of invasion with sulphate indicate a role for glycoproteins in this process. Our results suggest that treatment with antimetabolites may lead to a more aggressive phenotype by altering cell surface properties. 相似文献
52.
We describe RTblob, a high speed vision system that detects objects in cluttered scenes based on their color and shape at
a speed of over 800 frames/s. Because the system is available as open-source software and relies only on off-the-shelf PC
hardware components, it can provide the basis for multiple application scenarios. As an illustrative example, we show how
RTblob can be used in a robotic table tennis scenario to estimate ball trajectories through 3D space simultaneously from four
cameras images at a speed of 200 Hz. 相似文献
53.
hp-version finite elements for the space-time domain 总被引:1,自引:0,他引:1
A bilinear formulation of elasto-dynamics is offered which includes, as a special case, Hamilton's law of varying action. However, the more general bilinear formulation has several advantages over Hamilton's law. First, it admits a larger class of initial-value and boundary-value problems. Second, in its variational form, it offers physical insight into the so-called trailing terms of Hamilton's law. Third, numerical applications (i.e., finite elements in time) can be proven to be convergent under correct application of the bilinear formulation, whereas they can be demonstrated to diverge for specific problems under Hamilton's law. Fourth, the bilinear formulation offers automatic convergence of the natural velocity end conditions; while these must be constrained in present applications of Hamilton's law. Fifth, the bilinear formulation can be implemented in terms of a Larange multiplier that gives an order of magnitude improvement in the convergence of velocity. This implies that, in this form, the method is a hybrid finite-element approach.List of symbols
b
arbitrary constant
-
A
i, A
i
vector of integrals, i = 0, j
-
A()
linear operator on
-
()
Hamilton's form of A
-
B (u, )
bilinear operator u,
-
B (u, )
Hamilton's form of B
-
B
i,j
, B
ij
, B
ij
matrix of integrals
-
C
constant, N/m
-
c
number of floating-point operations per coef. evaluation
-
f, f(x)
force per unit length, N/m
-
F, F
0, F
L
forces, N
-
J
number of functions in series for û
-
k
spring rate per unit length, N/m2
-
K
spring rate, N/m
-
K
max
maximum value of K
-
L
a
Lagrangian, non-dimensional
-
L
length of beam, m
-
m
mass per unit length, kg/m
-
M
mass, kg
-
M
max
maximum value of M
-
n
number of functions in series for
-
N
number of elements in domain
-
p
momentum density, kg/sec
-
P, P
0, P
T
momentum, kg-m/sec
-
q
i
generalized coordinates
-
r
j
coefficients of
j
-
t
time, sec
-
t
0, t
1
limits of action integral, Hamilton's law
-
T
end of time period, sec
-
u
solution for displacement, m
-
û
approximation to u, m
-
u
0
initial value for u, m
-
test function, m
-
limited class of , m
-
x
spatial coordinate, m
-
flapping angle, rad
-
Lock number
-
time increment, sec
-
Lagrange multiplier
-
longitudinal stiffness EA, N (Eqs. 1–18)
-
advance ratio of rotor (Eqs. 33–34 and figures)
-
i
,
r
polynomial functions
-
non-dimensional time, azimuth angle
- ()
variation of ( )
- W
virtual work
- ( )
d ( )/dx
- ( .)
d ( )/dt
- (*)
d/d
- [ ]
matrix
- { }
column vector
-
row vector 相似文献
54.
We report on pulsed zero sound experiments in the B-phase of
3
He down to 0.6 mK. The investigated pressure and frequency range was 5 to 16 bar and 10 to 70 MHz, respectively. The dissipated energy during the sound pulses was between 0.4 to 90 nJ. The resolution in damping was about 0.1 cm
–1
. Within the range of our experimental parameters we never observed two phonon absorption resulting from non-linear coupling of zero sound to the J =2+ mode. However, with pulses of single frequency a new peak structure was found at temperatures corresponding to (T) = . This behavior is attributed to pair breaking by two phonons of the same energy. The attenuation increased with increasing pulse power, but also depended on pulse duration. In addition to that, we found at all pressures and frequencies an unreproducible attenuation structure close to the position of the J=2+ mode. 相似文献
55.
T. D. Dudderar C. P. Burger J. A. Gilbert J. A. Smith B. R. Peters 《Journal of Nondestructive Evaluation》1987,6(3):135-146
An innovative approach to nondestructive evaluation (NDE) using noncontacting optical sensors has demonstrated. In this effort a single mode optical fiber interferometer (OFI) was used to sense the presence and form of Rayleigh waves traveling along the surface of a steel test bar at a velocity of nearly 3mm/µs. Acousto-optic time-domain data was successfully used to detect the presence and locate the position of a test flaw (a machined slot) in the bar, and spectrum analysis was used to estimate its geometry and size. This approach has many potential applications in the ultrasonic evaluation of real flaws in structures with complex geometries. Coupled with the authors' earlier work demonstrating the feasibility of generating acoustic waves in metals using laser light pulses transmitted through the fiber optic probes, this latest achievement points to the development of a fully noncontacting, fiber optic based thermal-acousto-photonic (TAP) NDE system, with potential applications to the reliability testing of many important structures where composition, scale, geometry, or restricted access preclude the use of conventional NDE techniques. 相似文献
56.
Daniel Lam-Sidun Kia M. Peters Nica M. Borradaile 《International journal of molecular sciences》2021,22(6)
Medicinal use of mushrooms has been documented since ancient times, and in the modern world, mushrooms have a longstanding history of use in Eastern medicine. Recent interest in plant-based diets in Westernized countries has brought increasing attention to the use of mushrooms and mushroom-derived compounds in the prevention and treatment of chronic diseases. Edible mushrooms are the most abundant food sources of the modified amino acid, ergothioneine. This compound has been shown to accumulate in almost all cells and tissues, but preferentially in those exposed to oxidative stress and injury. The demonstrated cytoprotectant effect of ergothioneine has led many to suggest a potential therapeutic role for this compound in chronic conditions that involve ongoing oxidative stress and inflammation, including cardiovascular and metabolic diseases. However, the in vivo effects of ergothioneine and its underlying therapeutic mechanisms in the whole organism are not as clear. Moreover, there are no well-defined, clinical prevention and intervention trials of ergothioneine in chronic disease. This review highlights the cellular and molecular mechanisms of action of ergothioneine and its potential as a Traditional, Complementary and Alternative Medicine for the promotion of cardiometabolic health and the management of the most common manifestations of cardiometabolic disease. 相似文献
57.
Oliver Schmutzler Sebastian Graf Nils Behm Wael Y. Mansour Florian Blumendorf Theresa Staufer Christian Krnig Dina Salah Yanan Kang Jan N. Peters Yang Liu Neus Feliu Wolfgang J. Parak Anja Burkhardt Elisabetta Gargioni Sabrina Gennis Sharah Chandralingam Finn Heg Wolfgang Maison Kai Rothkamm Florian Schulz Florian Grüner 《International journal of molecular sciences》2021,22(7)
Quantitative cellular in vitro nanoparticle uptake measurements are possible with a large number of different techniques, however, all have their respective restrictions. Here, we demonstrate the application of synchrotron-based X-ray fluorescence imaging (XFI) on prostate tumor cells, which have internalized differently functionalized gold nanoparticles. Total nanoparticle uptake on the order of a few hundred picograms could be conveniently observed with microsamples consisting of only a few hundreds of cells. A comparison with mass spectroscopy quantification is provided, experimental results are both supported and sensitivity limits of this XFI approach extrapolated by Monte-Carlo simulations, yielding a minimum detectable nanoparticle mass of just 5 pg. This study demonstrates the high sensitivity level of XFI, allowing non-destructive uptake measurements with very small microsamples within just seconds of irradiation time. 相似文献
58.
Advances in Modeling and Simulation of Grinding Processes 总被引:6,自引:1,他引:6
E. Brinksmeier E. Govekar H.-W. Hoffmeister J. Peters D.J. Stephenson K. Weinert 《CIRP Annals》2006,55(2):667-696
In the last decade the relevance of modeling and simulation of grinding processes has significantly risen which is caused by industrial needs and is indicated by the number of publications and research activities in this area. This keynote paper results from a collaborative work within the STC G and gives an overview of the current state of the art in modeling and simulation of grinding processes: Physical process models (analytical and numerical models) and empirical process models (regression analysis, artificial neural net models) as well as heuristic process models (rule based models) are taken into account, and outlined with respect to their achievements in this paper. The models are characterized by the process parameters such as grinding force, grinding temperature, etc. as well as work results including surface topography and surface integrity. Furthermore, the capabilities and the limitations of the presented model types and simulation approaches will be exemplified. 相似文献
59.
A new concept for the processing and fabrication of rigid-rod molecular composites aiming at the elimination or minimization of phase separation is proposed. This approach calls for a coil-like aromatic polyisoimide which is soluble and compatible with an amorphous matrix polymer or thermosettable oligomer and can undergo facile transformation to the corresponding rigid-rod polyimide in solid composite state, thus imparting the inherently high strength/high modulus properties to the final form. To this end, various synthetic routes were explored to obtain para-diamines which could afford high molecular weight and aprotic-solvent-soluble polyisoimides upon polymerization with pyromellitic dianhydride (PMDA). Four such polyisoimides were prepared, with their inherent viscosities ranging from 0.25 to 1.89 dl g−1 in dimethylacetamide at 30°C. Facile thermally induced isoimide-imide conversion was demonstrated by solid-state (film) Fourier transform infrared spectroscopy. A preliminary evaluation of the compatibility of the polyisoimide/matrix resin was made. In one instance, a film prepared from the polyisoimide derived from PMDA and 3,3′,5,5′-tetramethylbenzidine (TMB) showed no visually detectable phase separation. 相似文献
60.
Condensation of 4–chloro–l, 8–naphthalic anhydride with 2–nitrophenol afforded 4–(2–nitrophenoxy)–l, 8–naphthalic anhydride, which on reduction followed by Pschorr intramolecular cyclisation gave benzo[k, l]xanthene–3, 4–dicarboxylic acid anhydride. The identity of the product was confirmed by its alternative synthesis from 5–amino–4–phenoxy–l, 8–naphthalic anhydride. Benzo[k, l]xanthene–3, 4–dicarbox–ylic acid anhydride condensed with alkylamines or arylamines and with o–phenylenediamines to yield the corresponding imides and imidazole derivatives, which coloured polyester in fluorescent greenish–yellow to orange hues, respectively, of good fastness to light and sublimation. The colour of the dyes is discussed with respect to analogous ring–closed sulphur– containing heterocycles. 相似文献