全文获取类型
收费全文 | 817篇 |
免费 | 110篇 |
国内免费 | 26篇 |
出版年
2024年 | 1篇 |
2023年 | 33篇 |
2022年 | 23篇 |
2021年 | 33篇 |
2020年 | 35篇 |
2019年 | 46篇 |
2018年 | 39篇 |
2017年 | 45篇 |
2016年 | 42篇 |
2015年 | 41篇 |
2014年 | 51篇 |
2013年 | 59篇 |
2012年 | 23篇 |
2011年 | 45篇 |
2010年 | 28篇 |
2009年 | 49篇 |
2008年 | 50篇 |
2007年 | 51篇 |
2006年 | 35篇 |
2005年 | 38篇 |
2004年 | 28篇 |
2003年 | 22篇 |
2002年 | 19篇 |
2001年 | 15篇 |
2000年 | 14篇 |
1999年 | 11篇 |
1998年 | 5篇 |
1997年 | 12篇 |
1996年 | 5篇 |
1995年 | 11篇 |
1994年 | 6篇 |
1993年 | 11篇 |
1992年 | 10篇 |
1991年 | 5篇 |
1990年 | 4篇 |
1989年 | 1篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1981年 | 1篇 |
排序方式: 共有953条查询结果,搜索用时 18 毫秒
1.
2.
《Bioorganic & medicinal chemistry letters》2020,30(17):127397
Herein, a boronic acid-based sensor was reported selectively to recognize Pd2+ ion. The fluorescence intensity increased 36-fold after sensor binding with 2.47 × 10−5 M of Pd2+ ion. It was carried out in the 99% aqueous solution for binding tests, indicating sensor having good water solubility. In addition, it is discernible that Pd2+ ion turned on the blue fluorescence of sensor under a UV–lamp (365 nm), while other ions (Ag+, Al3+, Ba2+, Ca2+, Cr2+, Cd2+, Co2+, Cs2+, Cu2+, Fe2+, Fe3+, K+, Li+, Mg2+, Mn2+, Na+, Ni2+ and Zn2+) did not show the similar change. Furthermore, sensor has a low limit of detection (38 nM) and high selectivity, which exhibits the potential for the development of Pd2+ recognition in practical environments. 相似文献
3.
This study aimed to prepare a novel quartz crystal microbalance (QCM) sensor for the detection of pirimicarb. Pirimicarb‐imprinted poly (ethylene glycol dimethacrylate‐N‐metacryloyl‐(l )‐tryptophan methyl ester) [p (EGDMA‐MATrp)] nanofilm (MIP) on the gold surface of a QCM chip was synthesized using the molecular imprinting technique. A nonimprinted p (EGDMA‐MATrp) nanofilm (NIP) was also synthesized using the same experimental technique. The MIP and NIP nanofilms were characterized via Fourier transform infrared spectroscopy attenuated total reflectance spectroscopy, contact angle, atomic force microscopy, and an ellipsometer. A competitive adsorption experiment on the sensor was performed to display the selectivity of the nanofilm. An analysis of the QCM sensor showed that the MIP nanofilm exhibited high sensitivity and selectivity for pirimicarb determination. A liquid chromatography‐tandem mass spectrometry method was prepared and validated to determine the accuracy and precision of the QCM sensor. The accuracy and precision of both methods were determined by a comparison of six replicates at three different concentrations to tomato samples extracted by using a Quick, Easy, Cheap, Effective, Rugged and Safe (QuEChERS) method. The limit of detection of the QCM sensor was found to be 0.028 nM. In conclusion, the QCM sensor showed good accuracy, with recovery percentages between 91 and 94%. Also, the pirimicarb‐imprinted QCM sensor exhibited a fast response time, reusability, high selectivity and sensitivity, and a low limit of detection. Therefore, it offers a serious alternative to the traditional analytical methods for pesticide detection in both natural sources and aqueous solutions. 相似文献
4.
Joseph W. Ndieyira Moyu Watari Rachel A. McKendry 《Journal of visualized experiments : JoVE》2013,(80)
The cantilever sensor, which acts as a transducer of reactions between model bacterial cell wall matrix immobilized on its surface and antibiotic drugs in solution, has shown considerable potential in biochemical sensing applications with unprecedented sensitivity and specificity1-5. The drug-target interactions generate surface stress, causing the cantilever to bend, and the signal can be analyzed optically when it is illuminated by a laser. The change in surface stress measured with nano-scale precision allows disruptions of the biomechanics of model bacterial cell wall targets to be tracked in real time. Despite offering considerable advantages, multiple cantilever sensor arrays have never been applied in quantifying drug-target binding interactions.Here, we report on the use of silicon multiple cantilever arrays coated with alkanethiol self-assembled monolayers mimicking bacterial cell wall matrix to quantitatively study antibiotic binding interactions. To understand the impact of vancomycin on the mechanics of bacterial cell wall structures1,6,7. We developed a new model1 which proposes that cantilever bending can be described by two independent factors; i) namely a chemical factor, which is given by a classical Langmuir adsorption isotherm, from which we calculate the thermodynamic equilibrium dissociation constant (Kd) and ii) a geometrical factor, essentially a measure of how bacterial peptide receptors are distributed on the cantilever surface. The surface distribution of peptide receptors (p) is used to investigate the dependence of geometry and ligand loading. It is shown that a threshold value of p ~10% is critical to sensing applications. Below which there is no detectable bending signal while above this value, the bending signal increases almost linearly, revealing that stress is a product of a local chemical binding factor and a geometrical factor combined by the mechanical connectivity of reacted regions and provides a new paradigm for design of powerful agents to combat superbug infections. 相似文献
5.
F. H. Dawson 《Hydrobiologia》1981,77(1):71-76
The design and characteristics of inexpensive and simply constructed equal-energy response photosynthetic irradiance sensors is described for use particularly where several cells are required in comparative ecological studies either above or below water. The dimensions of the sensors can be changed proportionally to suit different applications or components. The response of the sensor to irradiance at varying angles corresponds very closely to that required by the cosine law. The sensor is comparatively insensitive to other environmental variables in field use and gave a stable output; the long term drift was proportional to electrical output but in continuous use, drift is regular and could reach -0.08 year-1 of the total. The spectral range and cosine response is discussed in comparison to other more expensive (x 5–10) commercially available, sensors and to local standards. 相似文献
6.
A novel method for assessing the accuracy of inertial/magnetic sensors is presented. The method, referred to as the “residual matrix” method, is advantageous because it decouples the sensor's error with respect to Earth's gravity vector (attitude residual error: pitch and roll) from the sensor's error with respect to magnetic north (heading residual error), while remaining insensitive to singularity problems when the second Euler rotation is close to ±90°. As a demonstration, the accuracy of an inertial/magnetic sensor mounted to a participant's forearm was evaluated during a reaching task in a laboratory. Sensor orientation was measured internally (by the inertial/magnetic sensor) and externally using an optoelectronic measurement system with a marker cluster rigidly attached to the sensor's enclosure. Roll, pitch and heading residuals were calculated using the proposed novel method, as well as using a common orientation assessment method where the residuals are defined as the difference between the Euler angles measured by the inertial sensor and those measured by the optoelectronic system. Using the proposed residual matrix method, the roll and pitch residuals remained less than 1° and, as expected, no statistically significant difference between these two measures of attitude accuracy was found; the heading residuals were significantly larger than the attitude residuals but remained below 2°. Using the direct Euler angle comparison method, the residuals were in general larger due to singularity issues, and the expected significant difference between inertial/magnetic sensor attitude and heading accuracy was not present. 相似文献
7.
Environmental conditions differentially affect vir gene induction in different Agrobacterium strains. Role of the VirA sensor protein 总被引:3,自引:0,他引:3
S. C. J. Turk L. S. Melchers H. den Dulk-Ras A. J. G. Regensburg-Tuïnk P. J. J. Hooykaas 《Plant molecular biology》1991,16(6):1051-1059
The induction of vir gene expression in different types of Agrobacterium strains shows different pH sensitivity profiles. The pH sensitivity pattern demonstrated by octopine Ti strains was similar to that of a supervirulent leucinopine Ti strain, whereas this was different from that shown by nopaline Ti strains and agropine Ri strains. Data are given which indicate that these differences are due to different properties of the virA genes of these wild types. An exceptional case was formed by strains with the limited-host-range plasmid pTiAG57 which showed AS-dependent vir induction only if reduced inoculum sizes were used and the temperature was 28°C or below. 相似文献
8.
This work describes a new electrochemical sensor for hydrogen peroxide based on tin pentacyanonitrosylferrate (SnPCNF)-modified carbon ceramic electrode (CCE). The modified electrode was constructed by using a sol-gel technique involving two steps: construction of CCE containing metallic tin (Sn) powder and then electrochemical creation of SnPCNF film on the surface of CCE. The modified electrode was characterized by energy-dispersive X-ray, Fourier transform infrared, scanning electron microscopy, and cyclic voltammetry (CV) techniques. The charge transfer coefficient (α) and charge transfer rate constant (ks) for the modifying film were calculated. The electrocatalytic activity of the modified electrode toward the reduction of hydrogen peroxide was studied by CV and chronoamperometry. A linear calibration curve was obtained over the hydrogen peroxide concentration range of 0.5 to 69.4 μM using a hydrodynamic amperometric technique. The limit of detection (for a signal-to-noise ratio of 3) and sensitivity were found to be 92 nM and 0.89 μA/μM, respectively. Furthermore, the diffusion coefficient of hydrogen peroxide (D) and catalytic rate constant (kcat) were calculated. 相似文献
9.
10.
The NreB–NreC two-component system of Staphylococcus carnosus for O2 sensing cooperates with the accessory nitrate sensor NreA in the NreA–NreB–NreC system for coordinated sensing and regulation of nitrate respiration by O2 and nitrate. ApoNreA (NreA in the absence of nitrate) interacts with NreB and inhibits NreB autophosphorylation (and activation). NreB contains the phosphatase motif DxxxQ. The present study shows that NreB on its own was inactive for the dephosphorylation of the phosphorylated response regulator NreC (NreC-P), but co-incubation with NreB and NreA stimulated NreC-P dephosphorylation. Either the presence of instead of apoNreA or mutation of the phosphatase motif (D160 or Q164) of NreB abrogated phosphatase activity of NreB. Phosphatase activity was observed for anoxic (active) NreB as well as oxic NreB, therefore the functional state of NreB is not relevant for phosphatase activity. Thus, NreB is a bifunctional sensor kinase with an integral cryptic phosphatase activity. Activation of phosphatase activity and dephosphorylation of NreC-P requires NreA as a cofactor. Accordingly, NreA and nitrate have major and dual roles in NreA–NreB–NreC regulation by (i) inhibiting NreB phosphorylation and (ii) triggering a kinase/phosphatase switch of NreB when present as apoNreA. 相似文献